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 $214.92   12.345%   $241.4519   $241.45   $241.45   $241.50  
  Purchase #2 $119.29   5.243%   $125.5444   $125.54   $125.55   $125.50  
  Purchase #3 $43.27   12.736%   $48.7809   $48.78   $48.80   $48.80  
  Purchase #4 $74.62   13.629%   $84.79   $84.79   $84.80   $84.80  
  Purchase #5 $191.31   6.229%   $203.2267   $203.23   $203.25   $203.20  
  Purchase #6 $174.74   13.378%   $198.1167   $198.12   $198.10   $198.10  
  Purchase #7 $39.51   6.561%   $42.1023   $42.10   $42.10   $42.10  
  7 purchase totals = $857.66       $944.0129   $944.01   $944.05   $944.00