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 $87.67   10.416%   $96.8017   $96.80   $96.80   $96.80  
  Purchase #2 $142.34   12.378%   $159.9588   $159.96   $159.95   $160.00  
  Purchase #3 $136.62   7.441%   $146.7859   $146.79   $146.80   $146.80  
  Purchase #4 $140.65   6.459%   $149.7346   $149.73   $149.75   $149.70  
  Purchase #5 $182.85   13.338%   $207.2385   $207.24   $207.25   $207.20  
  Purchase #6 $42.99   8.517%   $46.6515   $46.65   $46.65   $46.70  
  Purchase #7 $236.46   7.429%   $254.0266   $254.03   $254.05   $254.00  
  7 purchase totals = $969.58       $1,061.1976   $1,061.20   $1,061.25   $1,061.20