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 $91.89   3.814%   $95.3947   $95.39   $95.40   $95.40  
  Purchase #2 $133.65   11.241%   $148.6736   $148.67   $148.65   $148.70  
  Purchase #3 $54.32   11.378%   $60.5005   $60.50   $60.50   $60.50  
  Purchase #4 $159.36   4.373%   $166.3288   $166.33   $166.35   $166.30  
  Purchase #5 $57.41   12.436%   $64.5495   $64.55   $64.55   $64.50  
  Purchase #6 $16.81   5.427%   $17.7223   $17.72   $17.70   $17.70  
  Purchase #7 $165.69   7.581%   $178.251   $178.25   $178.25   $178.30  
  7 purchase totals = $679.13       $731.4204   $731.41   $731.40   $731.40