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 $182.61   10.725%   $202.1949   $202.19   $202.20   $202.20  
  Purchase #2 $65.29   11.665%   $72.9061   $72.91   $72.90   $72.90  
  Purchase #3 $30.44   7.736%   $32.7948   $32.79   $32.80   $32.80  
  Purchase #4 $179.76   5.631%   $189.8823   $189.88   $189.90   $189.90  
  Purchase #5 $224.85   13.445%   $255.0811   $255.08   $255.10   $255.10  
  Purchase #6 $219.35   7.114%   $234.9546   $234.95   $234.95   $235.00  
  Purchase #7 $12.56   11.805%   $14.0427   $14.04   $14.05   $14.00  
  7 purchase totals = $914.86       $1,001.8565   $1,001.84   $1,001.90   $1,001.90