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 $201.85   8.829%   $219.6713   $219.67   $219.65   $219.70  
  Purchase #2 $83.46   12.772%   $94.1195   $94.12   $94.10   $94.10  
  Purchase #3 $27.63   7.509%   $29.7047   $29.70   $29.70   $29.70  
  Purchase #4 $90.98   8.433%   $98.6523   $98.65   $98.65   $98.70  
  Purchase #5 $183.84   10.838%   $203.7646   $203.76   $203.75   $203.80  
  Purchase #6 $192.81   7.554%   $207.3749   $207.37   $207.35   $207.40  
  Purchase #7 $141.48   5.768%   $149.6406   $149.64   $149.65   $149.60  
  7 purchase totals = $922.05       $1,002.9279   $1,002.91   $1,002.85   $1,003.00