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 $160.76   12.822%   $181.3726   $181.37   $181.35   $181.40  
  Purchase #2 $30.54   13.315%   $34.6064   $34.61   $34.60   $34.60  
  Purchase #3 $126.59   5.852%   $133.998   $134.00   $134.00   $134.00  
  Purchase #4 $162.46   10.205%   $179.039   $179.04   $179.05   $179.00  
  Purchase #5 $138.82   11.335%   $154.5552   $154.56   $154.55   $154.60  
  Purchase #6 $51.35   11.419%   $57.2137   $57.21   $57.20   $57.20  
  Purchase #7 $225.86   7.621%   $243.0728   $243.07   $243.05   $243.10  
  7 purchase totals = $896.38       $983.8577   $983.86   $983.80   $983.90