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 $191.58   9.194%   $209.1939   $209.19   $209.20   $209.20  
  Purchase #2 $94.78   8.452%   $102.7908   $102.79   $102.80   $102.80  
  Purchase #3 $134.43   10.740%   $148.8678   $148.87   $148.85   $148.90  
  Purchase #4 $207.76   5.633%   $219.4631   $219.46   $219.45   $219.50  
  Purchase #5 $221.58   11.477%   $247.0107   $247.01   $247.00   $247.00  
  Purchase #6 $45.81   4.145%   $47.7088   $47.71   $47.70   $47.70  
  Purchase #7 $42.41   10.318%   $46.7859   $46.79   $46.80   $46.80  
  7 purchase totals = $938.35       $1,021.8210   $1,021.82   $1,021.80   $1,021.90