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 $54.31   8.450%   $58.8992   $58.90   $58.90   $58.90  
  Purchase #2 $186.43   4.781%   $195.3432   $195.34   $195.35   $195.30  
  Purchase #3 $76.83   11.187%   $85.425   $85.43   $85.45   $85.40  
  Purchase #4 $46.97   12.140%   $52.6722   $52.67   $52.65   $52.70  
  Purchase #5 $154.71   12.822%   $174.5469   $174.55   $174.55   $174.50  
  Purchase #6 $244.93   9.202%   $267.4685   $267.47   $267.45   $267.50  
  Purchase #7 $185.94   6.206%   $197.4794   $197.48   $197.50   $197.50  
  7 purchase totals = $950.12       $1,031.8344   $1,031.84   $1,031.85   $1,031.80