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 $68.87   9.320%   $75.2887   $75.29   $75.30   $75.30  
  Purchase #2 $159.92   3.302%   $165.2006   $165.20   $165.20   $165.20  
  Purchase #3 $31.59   7.659%   $34.0095   $34.01   $34.00   $34.00  
  Purchase #4 $107.92   8.499%   $117.0921   $117.09   $117.10   $117.10  
  Purchase #5 $99.96   8.219%   $108.1757   $108.18   $108.20   $108.20  
  Purchase #6 $234.95   11.640%   $262.2982   $262.30   $262.30   $262.30  
  Purchase #7 $62.81   4.664%   $65.7395   $65.74   $65.75   $65.70  
  7 purchase totals = $766.02       $827.8043   $827.81   $827.85   $827.80