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 $119.70   3.745%   $124.1828   $124.18   $124.20   $124.20  
  Purchase #2 $12.32   9.325%   $13.4688   $13.47   $13.45   $13.50  
  Purchase #3 $75.31   10.417%   $83.155   $83.16   $83.15   $83.20  
  Purchase #4 $229.72   7.571%   $247.1121   $247.11   $247.10   $247.10  
  Purchase #5 $211.30   11.539%   $235.6819   $235.68   $235.70   $235.70  
  Purchase #6 $248.50   9.625%   $272.4181   $272.42   $272.40   $272.40  
  Purchase #7 $35.70   10.755%   $39.5395   $39.54   $39.55   $39.50  
  7 purchase totals = $932.55       $1,015.5582   $1,015.56   $1,015.55   $1,015.60