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 $65.28   6.386%   $69.4488   $69.45   $69.45   $69.40  
  Purchase #2 $183.88   11.476%   $204.9821   $204.98   $205.00   $205.00  
  Purchase #3 $59.57   8.517%   $64.6436   $64.64   $64.65   $64.60  
  Purchase #4 $90.89   7.736%   $97.9213   $97.92   $97.90   $97.90  
  Purchase #5 $12.95   11.373%   $14.4228   $14.42   $14.40   $14.40  
  Purchase #6 $247.41   13.678%   $281.2507   $281.25   $281.25   $281.30  
  Purchase #7 $148.68   11.512%   $165.796   $165.80   $165.80   $165.80  
  7 purchase totals = $808.66       $898.4653   $898.46   $898.45   $898.40