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 $61.57   7.737%   $66.3337   $66.33   $66.35   $66.30  
  Purchase #2 $123.60   13.413%   $140.1785   $140.18   $140.20   $140.20  
  Purchase #3 $155.36   11.779%   $173.6599   $173.66   $173.65   $173.70  
  Purchase #4 $47.68   3.292%   $49.2496   $49.25   $49.25   $49.20  
  Purchase #5 $232.96   10.775%   $258.0614   $258.06   $258.05   $258.10  
  Purchase #6 $148.91   9.477%   $163.0222   $163.02   $163.00   $163.00  
  Purchase #7 $170.94   7.480%   $183.7263   $183.73   $183.75   $183.70  
  7 purchase totals = $941.02       $1,034.2316   $1,034.23   $1,034.25   $1,034.20