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 $63.98   7.325%   $68.6665   $68.67   $68.65   $68.70  
  Purchase #2 $104.65   13.633%   $118.9169   $118.92   $118.90   $118.90  
  Purchase #3 $91.90   3.200%   $94.8408   $94.84   $94.85   $94.80  
  Purchase #4 $72.28   4.663%   $75.6504   $75.65   $75.65   $75.70  
  Purchase #5 $223.93   4.610%   $234.2532   $234.25   $234.25   $234.30  
  Purchase #6 $115.41   13.320%   $130.7826   $130.78   $130.80   $130.80  
  Purchase #7 $34.79   8.634%   $37.7938   $37.79   $37.80   $37.80  
  7 purchase totals = $706.94       $760.9042   $760.90   $760.90   $761.00