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 $80.72   9.712%   $88.5595   $88.56   $88.55   $88.60  
  Purchase #2 $55.59   6.111%   $58.9871   $58.99   $59.00   $59.00  
  Purchase #3 $94.90   8.236%   $102.716   $102.72   $102.70   $102.70  
  Purchase #4 $166.26   11.428%   $185.2602   $185.26   $185.25   $185.30  
  Purchase #5 $185.70   9.818%   $203.932   $203.93   $203.95   $203.90  
  Purchase #6 $120.98   12.341%   $135.9101   $135.91   $135.90   $135.90  
  Purchase #7 $18.32   10.684%   $20.2773   $20.28   $20.30   $20.30  
  7 purchase totals = $722.47       $795.6422   $795.65   $795.65   $795.70