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 $227.82   5.858%   $241.1657   $241.17   $241.15   $241.20  
  Purchase #2 $30.89   10.636%   $34.1755   $34.18   $34.20   $34.20  
  Purchase #3 $162.88   7.825%   $175.6254   $175.63   $175.65   $175.60  
  Purchase #4 $29.85   4.655%   $31.2395   $31.24   $31.25   $31.20  
  Purchase #5 $102.68   7.296%   $110.1715   $110.17   $110.15   $110.20  
  Purchase #6 $165.73   11.174%   $184.2487   $184.25   $184.25   $184.20  
  Purchase #7 $23.98   3.590%   $24.8409   $24.84   $24.85   $24.80  
  7 purchase totals = $743.83       $801.4672   $801.48   $801.50   $801.40