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 $129.43   4.104%   $134.7418   $134.74   $134.75   $134.70  
  Purchase #2 $196.41   3.105%   $202.5085   $202.51   $202.50   $202.50  
  Purchase #3 $108.32   12.766%   $122.1481   $122.15   $122.15   $122.10  
  Purchase #4 $93.41   12.590%   $105.1703   $105.17   $105.15   $105.20  
  Purchase #5 $243.87   7.584%   $262.3651   $262.37   $262.35   $262.40  
  Purchase #6 $35.71   9.160%   $38.981   $38.98   $39.00   $39.00  
  Purchase #7 $160.43   7.646%   $172.6965   $172.70   $172.70   $172.70  
  7 purchase totals = $967.58       $1,038.6113   $1,038.62   $1,038.60   $1,038.60