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 $61.81   12.185%   $69.3415   $69.34   $69.35   $69.30  
  Purchase #2 $78.36   5.676%   $82.8077   $82.81   $82.80   $82.80  
  Purchase #3 $86.92   9.108%   $94.8367   $94.84   $94.85   $94.80  
  Purchase #4 $217.42   13.722%   $247.2544   $247.25   $247.25   $247.30  
  Purchase #5 $141.88   5.235%   $149.3074   $149.31   $149.30   $149.30  
  Purchase #6 $148.78   12.702%   $167.678   $167.68   $167.70   $167.70  
  Purchase #7 $142.74   5.161%   $150.1068   $150.11   $150.10   $150.10  
  7 purchase totals = $877.91       $961.3325   $961.34   $961.35   $961.30