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 $24.84   3.752%   $25.772   $25.77   $25.75   $25.80  
  Purchase #2 $88.61   7.362%   $95.1335   $95.13   $95.15   $95.10  
  Purchase #3 $210.79   13.279%   $238.7808   $238.78   $238.80   $238.80  
  Purchase #4 $199.39   12.684%   $224.6806   $224.68   $224.70   $224.70  
  Purchase #5 $166.81   12.472%   $187.6145   $187.61   $187.60   $187.60  
  Purchase #6 $209.28   5.673%   $221.1525   $221.15   $221.15   $221.20  
  Purchase #7 $249.29   9.852%   $273.8501   $273.85   $273.85   $273.90  
  7 purchase totals = $1,149.01       $1,266.9840   $1,266.97   $1,267.00   $1,267.10