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 $128.52   12.479%   $144.558   $144.56   $144.55   $144.60  
  Purchase #2 $89.84   3.445%   $92.935   $92.94   $92.95   $92.90  
  Purchase #3 $149.76   6.104%   $158.9014   $158.90   $158.90   $158.90  
  Purchase #4 $204.78   10.361%   $225.9973   $226.00   $226.00   $226.00  
  Purchase #5 $187.66   13.800%   $213.5571   $213.56   $213.55   $213.60  
  Purchase #6 $245.66   3.253%   $253.6513   $253.65   $253.65   $253.70  
  Purchase #7 $170.74   7.552%   $183.6343   $183.63   $183.65   $183.60  
  7 purchase totals = $1,176.96       $1,273.2344   $1,273.24   $1,273.25   $1,273.30