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 $211.63   8.462%   $229.5381   $229.54   $229.55   $229.50  
  Purchase #2 $201.65   7.512%   $216.7979   $216.80   $216.80   $216.80  
  Purchase #3 $187.82   8.872%   $204.4834   $204.48   $204.50   $204.50  
  Purchase #4 $19.27   13.307%   $21.8343   $21.83   $21.85   $21.80  
  Purchase #5 $198.61   8.783%   $216.0539   $216.05   $216.05   $216.10  
  Purchase #6 $49.70   7.808%   $53.5806   $53.58   $53.60   $53.60  
  Purchase #7 $172.56   4.767%   $180.7859   $180.79   $180.80   $180.80  
  7 purchase totals = $1,041.24       $1,123.0741   $1,123.07   $1,123.15   $1,123.10