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 $46.37   4.310%   $48.3685   $48.37   $48.35   $48.40  
  Purchase #2 $131.94   12.845%   $148.8877   $148.89   $148.90   $148.90  
  Purchase #3 $176.50   12.588%   $198.7178   $198.72   $198.70   $198.70  
  Purchase #4 $23.27   11.512%   $25.9488   $25.95   $25.95   $25.90  
  Purchase #5 $161.92   4.821%   $169.7262   $169.73   $169.75   $169.70  
  Purchase #6 $188.74   5.256%   $198.6602   $198.66   $198.65   $198.70  
  Purchase #7 $247.67   8.176%   $267.9195   $267.92   $267.90   $267.90  
  7 purchase totals = $976.41       $1,058.2287   $1,058.24   $1,058.20   $1,058.20