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 $199.56   7.380%   $214.2875   $214.29   $214.30   $214.30  
  Purchase #2 $148.45   8.394%   $160.9109   $160.91   $160.90   $160.90  
  Purchase #3 $57.64   5.592%   $60.8632   $60.86   $60.85   $60.90  
  Purchase #4 $166.77   3.282%   $172.2434   $172.24   $172.25   $172.20  
  Purchase #5 $112.31   4.425%   $117.2797   $117.28   $117.30   $117.30  
  Purchase #6 $186.29   11.224%   $207.1992   $207.20   $207.20   $207.20  
  Purchase #7 $51.85   4.203%   $54.0293   $54.03   $54.05   $54.00  
  7 purchase totals = $922.87       $986.8132   $986.81   $986.85   $986.80