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 $246.63   3.471%   $255.1905   $255.19   $255.20   $255.20  
  Purchase #2 $208.65   5.760%   $220.6682   $220.67   $220.65   $220.70  
  Purchase #3 $62.25   13.644%   $70.7434   $70.74   $70.75   $70.70  
  Purchase #4 $175.64   3.297%   $181.4309   $181.43   $181.45   $181.40  
  Purchase #5 $245.32   4.266%   $255.7854   $255.79   $255.80   $255.80  
  Purchase #6 $145.84   4.662%   $152.6391   $152.64   $152.65   $152.60  
  Purchase #7 $89.73   4.139%   $93.4439   $93.44   $93.45   $93.40  
  7 purchase totals = $1,174.06       $1,229.9014   $1,229.90   $1,229.95   $1,229.80