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 $47.71   8.443%   $51.7382   $51.74   $51.75   $51.70  
  Purchase #2 $241.88   5.412%   $254.9705   $254.97   $254.95   $255.00  
  Purchase #3 $242.64   10.859%   $268.9883   $268.99   $269.00   $269.00  
  Purchase #4 $191.51   5.168%   $201.4072   $201.41   $201.40   $201.40  
  Purchase #5 $24.67   6.783%   $26.3434   $26.34   $26.35   $26.30  
  Purchase #6 $197.88   10.814%   $219.2787   $219.28   $219.30   $219.30  
  Purchase #7 $209.46   5.723%   $221.4474   $221.45   $221.45   $221.40  
  7 purchase totals = $1,155.75       $1,244.1737   $1,244.18   $1,244.20   $1,244.10