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 $198.41   5.346%   $209.017   $209.02   $209.00   $209.00  
  Purchase #2 $87.75   5.660%   $92.7167   $92.72   $92.70   $92.70  
  Purchase #3 $122.71   8.829%   $133.5441   $133.54   $133.55   $133.50  
  Purchase #4 $32.61   3.488%   $33.7474   $33.75   $33.75   $33.70  
  Purchase #5 $57.52   9.856%   $63.1892   $63.19   $63.20   $63.20  
  Purchase #6 $167.82   11.796%   $187.616   $187.62   $187.60   $187.60  
  Purchase #7 $218.74   11.486%   $243.8645   $243.86   $243.85   $243.90  
  7 purchase totals = $885.56       $963.6949   $963.70   $963.65   $963.60