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 $72.80   9.550%   $79.7524   $79.75   $79.75   $79.80  
  Purchase #2 $242.77   3.136%   $250.3833   $250.38   $250.40   $250.40  
  Purchase #3 $113.93   11.652%   $127.2051   $127.21   $127.20   $127.20  
  Purchase #4 $10.66   7.123%   $11.4193   $11.42   $11.40   $11.40  
  Purchase #5 $29.78   4.776%   $31.2023   $31.20   $31.20   $31.20  
  Purchase #6 $26.36   4.397%   $27.519   $27.52   $27.50   $27.50  
  Purchase #7 $209.81   11.758%   $234.4795   $234.48   $234.50   $234.50  
  7 purchase totals = $706.11       $761.9609   $761.96   $761.95   $762.00