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 $88.66   10.179%   $97.6847   $97.68   $97.70   $97.70  
  Purchase #2 $52.71   5.690%   $55.7092   $55.71   $55.70   $55.70  
  Purchase #3 $108.82   12.672%   $122.6097   $122.61   $122.60   $122.60  
  Purchase #4 $194.50   5.632%   $205.4542   $205.45   $205.45   $205.50  
  Purchase #5 $5.26   12.587%   $5.9221   $5.92   $5.90   $5.90  
  Purchase #6 $73.80   4.480%   $77.1062   $77.11   $77.10   $77.10  
  Purchase #7 $215.86   11.674%   $241.0595   $241.06   $241.05   $241.10  
  7 purchase totals = $739.61       $805.5456   $805.54   $805.50   $805.60