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 $60.90   5.380%   $64.1764   $64.18   $64.20   $64.20  
  Purchase #2 $230.99   12.384%   $259.5958   $259.60   $259.60   $259.60  
  Purchase #3 $246.94   8.270%   $267.3619   $267.36   $267.35   $267.40  
  Purchase #4 $194.89   4.802%   $204.2486   $204.25   $204.25   $204.20  
  Purchase #5 $63.46   3.306%   $65.558   $65.56   $65.55   $65.60  
  Purchase #6 $73.94   9.719%   $81.1262   $81.13   $81.15   $81.10  
  Purchase #7 $5.82   9.692%   $6.3841   $6.38   $6.40   $6.40  
  7 purchase totals = $876.94       $948.4510   $948.46   $948.50   $948.50