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 $117.82   13.702%   $133.9637   $133.96   $133.95   $134.00  
  Purchase #2 $77.42   12.207%   $86.8707   $86.87   $86.85   $86.90  
  Purchase #3 $153.71   10.807%   $170.3214   $170.32   $170.30   $170.30  
  Purchase #4 $185.44   12.802%   $209.18   $209.18   $209.20   $209.20  
  Purchase #5 $162.92   12.844%   $183.8454   $183.85   $183.85   $183.80  
  Purchase #6 $151.44   6.195%   $160.8217   $160.82   $160.80   $160.80  
  Purchase #7 $116.31   7.582%   $125.1286   $125.13   $125.15   $125.10  
  7 purchase totals = $965.06       $1,070.1315   $1,070.13   $1,070.10   $1,070.10