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 $205.26   9.873%   $225.5253   $225.53   $225.55   $225.50  
  Purchase #2 $105.52   12.752%   $118.9759   $118.98   $119.00   $119.00  
  Purchase #3 $40.35   13.621%   $45.8461   $45.85   $45.85   $45.80  
  Purchase #4 $85.53   3.550%   $88.5663   $88.57   $88.55   $88.60  
  Purchase #5 $83.26   12.748%   $93.874   $93.87   $93.85   $93.90  
  Purchase #6 $126.85   8.378%   $137.4775   $137.48   $137.50   $137.50  
  Purchase #7 $154.73   6.450%   $164.7101   $164.71   $164.70   $164.70  
  7 purchase totals = $801.50       $874.9752   $874.99   $875.00   $875.00