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 $124.58   13.457%   $141.3447   $141.34   $141.35   $141.30  
  Purchase #2 $169.39   6.251%   $179.9786   $179.98   $180.00   $180.00  
  Purchase #3 $214.31   12.259%   $240.5823   $240.58   $240.60   $240.60  
  Purchase #4 $219.69   6.591%   $234.1698   $234.17   $234.15   $234.20  
  Purchase #5 $23.37   5.750%   $24.7138   $24.71   $24.70   $24.70  
  Purchase #6 $50.69   10.249%   $55.8852   $55.89   $55.90   $55.90  
  Purchase #7 $23.57   4.634%   $24.6622   $24.66   $24.65   $24.70  
  7 purchase totals = $825.60       $901.3366   $901.33   $901.35   $901.40