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 $235.66   4.273%   $245.7298   $245.73   $245.75   $245.70  
  Purchase #2 $80.34   8.319%   $87.0235   $87.02   $87.00   $87.00  
  Purchase #3 $187.63   10.377%   $207.1004   $207.10   $207.10   $207.10  
  Purchase #4 $68.43   4.676%   $71.6298   $71.63   $71.65   $71.60  
  Purchase #5 $224.53   10.844%   $248.878   $248.88   $248.90   $248.90  
  Purchase #6 $187.99   3.221%   $194.0452   $194.05   $194.05   $194.00  
  Purchase #7 $138.70   7.130%   $148.5893   $148.59   $148.60   $148.60  
  7 purchase totals = $1,123.28       $1,202.9960   $1,203.00   $1,203.05   $1,202.90