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 $241.50   12.203%   $270.9702   $270.97   $270.95   $271.00  
  Purchase #2 $136.39   12.764%   $153.7988   $153.80   $153.80   $153.80  
  Purchase #3 $182.61   3.318%   $188.669   $188.67   $188.65   $188.70  
  Purchase #4 $63.37   8.187%   $68.5581   $68.56   $68.55   $68.60  
  Purchase #5 $203.75   13.192%   $230.6287   $230.63   $230.65   $230.60  
  Purchase #6 $213.59   4.872%   $223.9961   $224.00   $224.00   $224.00  
  Purchase #7 $23.61   5.469%   $24.9012   $24.90   $24.90   $24.90  
  7 purchase totals = $1,064.82       $1,161.5221   $1,161.53   $1,161.50   $1,161.60