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 $182.25   13.432%   $206.7298   $206.73   $206.75   $206.70  
  Purchase #2 $55.65   13.107%   $62.944   $62.94   $62.95   $62.90  
  Purchase #3 $22.81   11.684%   $25.4751   $25.48   $25.50   $25.50  
  Purchase #4 $193.86   8.123%   $209.6072   $209.61   $209.60   $209.60  
  Purchase #5 $74.31   8.483%   $80.6137   $80.61   $80.60   $80.60  
  Purchase #6 $245.63   5.267%   $258.5673   $258.57   $258.55   $258.60  
  Purchase #7 $23.97   6.513%   $25.5312   $25.53   $25.55   $25.50  
  7 purchase totals = $798.48       $869.4683   $869.47   $869.50   $869.40