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 $154.91   7.562%   $166.6243   $166.62   $166.60   $166.60  
  Purchase #2 $191.62   12.180%   $214.9593   $214.96   $214.95   $215.00  
  Purchase #3 $5.37   11.285%   $5.976   $5.98   $6.00   $6.00  
  Purchase #4 $30.95   8.442%   $33.5628   $33.56   $33.55   $33.60  
  Purchase #5 $210.25   9.691%   $230.6253   $230.63   $230.65   $230.60  
  Purchase #6 $64.48   3.482%   $66.7252   $66.73   $66.75   $66.70  
  Purchase #7 $48.98   10.662%   $54.2022   $54.20   $54.20   $54.20  
  7 purchase totals = $706.56       $772.6751   $772.68   $772.70   $772.70