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 $239.82   11.624%   $267.6967   $267.70   $267.70   $267.70  
  Purchase #2 $129.80   12.219%   $145.6603   $145.66   $145.65   $145.70  
  Purchase #3 $60.98   8.236%   $66.0023   $66.00   $66.00   $66.00  
  Purchase #4 $237.83   7.778%   $256.3284   $256.33   $256.35   $256.30  
  Purchase #5 $171.30   3.757%   $177.7357   $177.74   $177.75   $177.70  
  Purchase #6 $66.92   6.127%   $71.0202   $71.02   $71.00   $71.00  
  Purchase #7 $147.72   11.712%   $165.021   $165.02   $165.00   $165.00  
  7 purchase totals = $1,054.37       $1,149.4646   $1,149.47   $1,149.45   $1,149.40