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 $58.79   8.775%   $63.9488   $63.95   $63.95   $63.90  
  Purchase #2 $77.75   7.851%   $83.8542   $83.85   $83.85   $83.90  
  Purchase #3 $183.91   11.455%   $204.9769   $204.98   $205.00   $205.00  
  Purchase #4 $231.61   6.177%   $245.9165   $245.92   $245.90   $245.90  
  Purchase #5 $34.78   8.318%   $37.673   $37.67   $37.65   $37.70  
  Purchase #6 $223.68   9.119%   $244.0774   $244.08   $244.10   $244.10  
  Purchase #7 $113.84   10.642%   $125.9549   $125.95   $125.95   $126.00  
  7 purchase totals = $924.36       $1,006.4017   $1,006.40   $1,006.40   $1,006.50