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 $64.97   13.755%   $73.9066   $73.91   $73.90   $73.90  
  Purchase #2 $212.67   9.153%   $232.1357   $232.14   $232.15   $232.10  
  Purchase #3 $78.84   6.505%   $83.9685   $83.97   $83.95   $84.00  
  Purchase #4 $99.86   6.265%   $106.1162   $106.12   $106.10   $106.10  
  Purchase #5 $183.84   6.782%   $196.308   $196.31   $196.30   $196.30  
  Purchase #6 $220.60   3.435%   $228.1776   $228.18   $228.20   $228.20  
  Purchase #7 $180.46   7.658%   $194.2796   $194.28   $194.30   $194.30  
  7 purchase totals = $1,041.24       $1,114.8922   $1,114.91   $1,114.90   $1,114.90