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 $194.79   6.117%   $206.7053   $206.71   $206.70   $206.70  
  Purchase #2 $101.74   8.498%   $110.3859   $110.39   $110.40   $110.40  
  Purchase #3 $24.69   4.852%   $25.888   $25.89   $25.90   $25.90  
  Purchase #4 $178.35   12.696%   $200.9933   $200.99   $201.00   $201.00  
  Purchase #5 $197.97   11.590%   $220.9147   $220.91   $220.90   $220.90  
  Purchase #6 $123.84   7.309%   $132.8915   $132.89   $132.90   $132.90  
  Purchase #7 $105.50   11.475%   $117.6061   $117.61   $117.60   $117.60  
  7 purchase totals = $926.88       $1,015.3848   $1,015.39   $1,015.40   $1,015.40