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 $190.96   7.333%   $204.9631   $204.96   $204.95   $205.00  
  Purchase #2 $202.47   13.285%   $229.3681   $229.37   $229.35   $229.40  
  Purchase #3 $5.55   12.553%   $6.2467   $6.25   $6.25   $6.20  
  Purchase #4 $91.27   10.842%   $101.1655   $101.17   $101.15   $101.20  
  Purchase #5 $194.93   8.721%   $211.9298   $211.93   $211.95   $211.90  
  Purchase #6 $219.53   12.736%   $247.4893   $247.49   $247.50   $247.50  
  Purchase #7 $15.61   12.178%   $17.511   $17.51   $17.50   $17.50  
  7 purchase totals = $920.32       $1,018.6735   $1,018.68   $1,018.65   $1,018.70