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 $62.51   12.681%   $70.4369   $70.44   $70.45   $70.40  
  Purchase #2 $228.33   8.152%   $246.9435   $246.94   $246.95   $246.90  
  Purchase #3 $185.70   10.237%   $204.7101   $204.71   $204.70   $204.70  
  Purchase #4 $105.89   10.108%   $116.5934   $116.59   $116.60   $116.60  
  Purchase #5 $87.28   10.383%   $96.3423   $96.34   $96.35   $96.30  
  Purchase #6 $229.68   9.162%   $250.7233   $250.72   $250.70   $250.70  
  Purchase #7 $166.33   8.797%   $180.9621   $180.96   $180.95   $181.00  
  7 purchase totals = $1,065.72       $1,166.7116   $1,166.70   $1,166.70   $1,166.60