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 $89.91   3.744%   $93.2762   $93.28   $93.30   $93.30  
  Purchase #2 $247.60   8.123%   $267.7125   $267.71   $267.70   $267.70  
  Purchase #3 $165.29   10.340%   $182.381   $182.38   $182.40   $182.40  
  Purchase #4 $212.70   13.269%   $240.9232   $240.92   $240.90   $240.90  
  Purchase #5 $87.50   9.334%   $95.6673   $95.67   $95.65   $95.70  
  Purchase #6 $131.88   10.752%   $146.0597   $146.06   $146.05   $146.10  
  Purchase #7 $29.57   6.166%   $31.3933   $31.39   $31.40   $31.40  
  7 purchase totals = $964.45       $1,057.4132   $1,057.41   $1,057.40   $1,057.50