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 $86.58   13.655%   $98.4025   $98.40   $98.40   $98.40  
  Purchase #2 $131.54   7.330%   $141.1819   $141.18   $141.20   $141.20  
  Purchase #3 $29.90   11.457%   $33.3256   $33.33   $33.35   $33.30  
  Purchase #4 $96.35   6.569%   $102.6792   $102.68   $102.70   $102.70  
  Purchase #5 $194.65   8.368%   $210.9383   $210.94   $210.95   $210.90  
  Purchase #6 $209.97   5.747%   $222.037   $222.04   $222.05   $222.00  
  Purchase #7 $42.62   3.250%   $44.0052   $44.01   $44.00   $44.00  
  7 purchase totals = $791.61       $852.5697   $852.58   $852.65   $852.50