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 $144.39   6.543%   $153.8374   $153.84   $153.85   $153.80  
  Purchase #2 $201.51   3.716%   $208.9981   $209.00   $209.00   $209.00  
  Purchase #3 $104.57   3.470%   $108.1986   $108.20   $108.20   $108.20  
  Purchase #4 $211.38   10.128%   $232.7886   $232.79   $232.80   $232.80  
  Purchase #5 $167.68   3.826%   $174.0954   $174.10   $174.10   $174.10  
  Purchase #6 $236.73   11.319%   $263.5255   $263.53   $263.55   $263.50  
  Purchase #7 $188.33   10.679%   $208.4418   $208.44   $208.45   $208.40  
  7 purchase totals = $1,254.59       $1,349.8854   $1,349.90   $1,349.95   $1,349.80