Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $224.78   4.542%   $234.9895   $234.99   $235.00   $235.00  
  Purchase #2 $150.56   13.278%   $170.5514   $170.55   $170.55   $170.60  
  Purchase #3 $185.96   7.764%   $200.3979   $200.40   $200.40   $200.40  
  Purchase #4 $218.27   4.606%   $228.3235   $228.32   $228.30   $228.30  
  Purchase #5 $189.54   12.357%   $212.9615   $212.96   $212.95   $213.00  
  Purchase #6 $194.64   9.784%   $213.6836   $213.68   $213.70   $213.70  
  Purchase #7 $181.44   13.576%   $206.0723   $206.07   $206.05   $206.10  
  7 purchase totals = $1,345.19       $1,466.9797   $1,466.97   $1,466.95   $1,467.10