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 $14.76   13.326%   $16.7269   $16.73   $16.75   $16.70  
  Purchase #2 $32.96   10.283%   $36.3493   $36.35   $36.35   $36.30  
  Purchase #3 $85.53   3.503%   $88.5261   $88.53   $88.55   $88.50  
  Purchase #4 $16.63   12.185%   $18.6564   $18.66   $18.65   $18.70  
  Purchase #5 $196.59   7.606%   $211.5426   $211.54   $211.55   $211.50  
  Purchase #6 $230.58   6.397%   $245.3302   $245.33   $245.35   $245.30  
  Purchase #7 $244.92   4.543%   $256.0467   $256.05   $256.05   $256.00  
  7 purchase totals = $821.97       $873.1782   $873.19   $873.25   $873.00