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 $71.46   6.414%   $76.0434   $76.04   $76.05   $76.00  
  Purchase #2 $134.62   8.204%   $145.6642   $145.66   $145.65   $145.70  
  Purchase #3 $106.25   5.566%   $112.1639   $112.16   $112.15   $112.20  
  Purchase #4 $23.72   9.503%   $25.9741   $25.97   $25.95   $26.00  
  Purchase #5 $76.72   12.469%   $86.2862   $86.29   $86.30   $86.30  
  Purchase #6 $99.42   6.129%   $105.5135   $105.51   $105.50   $105.50  
  Purchase #7 $187.25   9.267%   $204.6025   $204.60   $204.60   $204.60  
  7 purchase totals = $699.44       $756.2478   $756.23   $756.20   $756.30