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 $246.30   6.825%   $263.11   $263.11   $263.10   $263.10  
  Purchase #2 $116.71   5.163%   $122.7357   $122.74   $122.75   $122.70  
  Purchase #3 $160.82   8.362%   $174.2678   $174.27   $174.25   $174.30  
  Purchase #4 $33.76   12.129%   $37.8548   $37.85   $37.85   $37.90  
  Purchase #5 $9.99   7.273%   $10.7166   $10.72   $10.70   $10.70  
  Purchase #6 $209.78   7.447%   $225.4023   $225.40   $225.40   $225.40  
  Purchase #7 $83.37   6.692%   $88.9491   $88.95   $88.95   $88.90  
  7 purchase totals = $860.73       $923.0363   $923.04   $923.00   $923.00