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 $154.26   6.761%   $164.6895   $164.69   $164.70   $164.70  
  Purchase #2 $221.92   11.504%   $247.4497   $247.45   $247.45   $247.40  
  Purchase #3 $243.42   7.141%   $260.8026   $260.80   $260.80   $260.80  
  Purchase #4 $223.89   10.628%   $247.685   $247.69   $247.70   $247.70  
  Purchase #5 $22.52   8.777%   $24.4966   $24.50   $24.50   $24.50  
  Purchase #6 $127.53   9.484%   $139.6249   $139.62   $139.60   $139.60  
  Purchase #7 $30.26   7.530%   $32.5386   $32.54   $32.55   $32.50  
  7 purchase totals = $1,023.80       $1,117.2869   $1,117.29   $1,117.30   $1,117.20