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 $215.76   3.346%   $222.9793   $222.98   $223.00   $223.00  
  Purchase #2 $70.79   11.813%   $79.1524   $79.15   $79.15   $79.20  
  Purchase #3 $216.89   11.530%   $241.8974   $241.90   $241.90   $241.90  
  Purchase #4 $112.73   9.858%   $123.8429   $123.84   $123.85   $123.80  
  Purchase #5 $99.32   3.324%   $102.6214   $102.62   $102.60   $102.60  
  Purchase #6 $215.26   4.572%   $225.1017   $225.10   $225.10   $225.10  
  Purchase #7 $34.30   5.772%   $36.2798   $36.28   $36.30   $36.30  
  7 purchase totals = $965.05       $1,031.8749   $1,031.87   $1,031.90   $1,031.90