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 $83.94   3.578%   $86.9434   $86.94   $86.95   $86.90  
  Purchase #2 $136.66   13.487%   $155.0913   $155.09   $155.10   $155.10  
  Purchase #3 $123.92   6.802%   $132.349   $132.35   $132.35   $132.30  
  Purchase #4 $69.53   8.874%   $75.7001   $75.70   $75.70   $75.70  
  Purchase #5 $174.91   10.865%   $193.914   $193.91   $193.90   $193.90  
  Purchase #6 $34.75   10.360%   $38.3501   $38.35   $38.35   $38.40  
  Purchase #7 $82.55   10.497%   $91.2153   $91.22   $91.20   $91.20  
  7 purchase totals = $706.26       $773.5632   $773.56   $773.55   $773.50