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 $94.67   8.370%   $102.5939   $102.59   $102.60   $102.60  
  Purchase #2 $146.70   13.791%   $166.9314   $166.93   $166.95   $166.90  
  Purchase #3 $201.75   13.123%   $228.2257   $228.23   $228.25   $228.20  
  Purchase #4 $22.95   5.665%   $24.2501   $24.25   $24.25   $24.30  
  Purchase #5 $183.29   8.804%   $199.4269   $199.43   $199.45   $199.40  
  Purchase #6 $240.46   8.231%   $260.2523   $260.25   $260.25   $260.30  
  Purchase #7 $150.98   5.521%   $159.3156   $159.32   $159.30   $159.30  
  7 purchase totals = $1,040.80       $1,140.9959   $1,141.00   $1,141.05   $1,141.00