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 $87.48   8.411%   $94.8379   $94.84   $94.85   $94.80  
  Purchase #2 $195.34   13.227%   $221.1776   $221.18   $221.20   $221.20  
  Purchase #3 $149.75   11.716%   $167.2947   $167.29   $167.30   $167.30  
  Purchase #4 $188.90   7.600%   $203.2564   $203.26   $203.25   $203.30  
  Purchase #5 $75.29   3.578%   $77.9839   $77.98   $78.00   $78.00  
  Purchase #6 $55.38   10.775%   $61.3472   $61.35   $61.35   $61.30  
  Purchase #7 $209.53   6.760%   $223.6942   $223.69   $223.70   $223.70  
  7 purchase totals = $961.67       $1,049.5919   $1,049.59   $1,049.65   $1,049.60