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 $31.92   5.729%   $33.7487   $33.75   $33.75   $33.70  
  Purchase #2 $211.86   6.808%   $226.2834   $226.28   $226.30   $226.30  
  Purchase #3 $162.85   7.203%   $174.5801   $174.58   $174.60   $174.60  
  Purchase #4 $233.81   10.678%   $258.7762   $258.78   $258.80   $258.80  
  Purchase #5 $6.72   6.345%   $7.1464   $7.15   $7.15   $7.10  
  Purchase #6 $202.86   3.183%   $209.317   $209.32   $209.30   $209.30  
  Purchase #7 $62.54   12.496%   $70.355   $70.36   $70.35   $70.40  
  7 purchase totals = $912.56       $980.2068   $980.22   $980.25   $980.20