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 $58.28   10.704%   $64.5183   $64.52   $64.50   $64.50  
  Purchase #2 $60.67   12.488%   $68.2465   $68.25   $68.25   $68.20  
  Purchase #3 $180.37   9.587%   $197.6621   $197.66   $197.65   $197.70  
  Purchase #4 $205.44   9.623%   $225.2095   $225.21   $225.20   $225.20  
  Purchase #5 $75.68   11.691%   $84.5277   $84.53   $84.55   $84.50  
  Purchase #6 $237.83   12.391%   $267.2995   $267.30   $267.30   $267.30  
  Purchase #7 $72.54   7.213%   $77.7723   $77.77   $77.75   $77.80  
  7 purchase totals = $890.81       $985.2359   $985.24   $985.20   $985.20