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 $229.39   11.684%   $256.1919   $256.19   $256.20   $256.20  
  Purchase #2 $58.61   6.354%   $62.3341   $62.33   $62.35   $62.30  
  Purchase #3 $90.30   8.247%   $97.747   $97.75   $97.75   $97.70  
  Purchase #4 $226.32   13.658%   $257.2308   $257.23   $257.25   $257.20  
  Purchase #5 $57.33   5.834%   $60.6746   $60.67   $60.65   $60.70  
  Purchase #6 $144.33   7.357%   $154.9484   $154.95   $154.95   $154.90  
  Purchase #7 $132.37   9.505%   $144.9518   $144.95   $144.95   $145.00  
  7 purchase totals = $938.65       $1,034.0786   $1,034.07   $1,034.10   $1,034.00