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 $52.89   11.470%   $58.9565   $58.96   $58.95   $59.00  
  Purchase #2 $87.26   6.788%   $93.1832   $93.18   $93.20   $93.20  
  Purchase #3 $8.60   11.468%   $9.5862   $9.59   $9.60   $9.60  
  Purchase #4 $243.96   8.344%   $264.316   $264.32   $264.30   $264.30  
  Purchase #5 $195.27   9.357%   $213.5414   $213.54   $213.55   $213.50  
  Purchase #6 $137.87   7.456%   $148.1496   $148.15   $148.15   $148.10  
  Purchase #7 $14.81   9.160%   $16.1666   $16.17   $16.15   $16.20  
  7 purchase totals = $740.66       $803.8995   $803.91   $803.90   $803.90