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 $62.33   11.111%   $69.2555   $69.26   $69.25   $69.30  
  Purchase #2 $164.99   9.148%   $180.0833   $180.08   $180.10   $180.10  
  Purchase #3 $61.79   4.637%   $64.6552   $64.66   $64.65   $64.70  
  Purchase #4 $109.97   11.399%   $122.5055   $122.51   $122.50   $122.50  
  Purchase #5 $16.92   12.273%   $18.9966   $19.00   $19.00   $19.00  
  Purchase #6 $97.91   5.123%   $102.9259   $102.93   $102.95   $102.90  
  Purchase #7 $205.51   9.296%   $224.6142   $224.61   $224.60   $224.60  
  7 purchase totals = $719.42       $783.0362   $783.05   $783.05   $783.10