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 $244.35   12.383%   $274.6079   $274.61   $274.60   $274.60  
  Purchase #2 $64.77   7.632%   $69.7132   $69.71   $69.70   $69.70  
  Purchase #3 $41.67   5.708%   $44.0485   $44.05   $44.05   $44.00  
  Purchase #4 $226.41   7.743%   $243.9409   $243.94   $243.95   $243.90  
  Purchase #5 $241.93   11.743%   $270.3398   $270.34   $270.35   $270.30  
  Purchase #6 $32.66   13.437%   $37.0485   $37.05   $37.05   $37.00  
  Purchase #7 $43.87   3.410%   $45.366   $45.37   $45.35   $45.40  
  7 purchase totals = $895.66       $985.0648   $985.07   $985.05   $984.90