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 $88.98   4.830%   $93.2777   $93.28   $93.30   $93.30  
  Purchase #2 $238.81   12.199%   $267.9424   $267.94   $267.95   $267.90  
  Purchase #3 $236.68   7.178%   $253.6689   $253.67   $253.65   $253.70  
  Purchase #4 $82.97   3.111%   $85.5512   $85.55   $85.55   $85.60  
  Purchase #5 $77.99   8.174%   $84.3649   $84.36   $84.35   $84.40  
  Purchase #6 $141.66   8.602%   $153.8456   $153.85   $153.85   $153.80  
  Purchase #7 $86.64   4.648%   $90.667   $90.67   $90.65   $90.70  
  7 purchase totals = $953.73       $1,029.3177   $1,029.32   $1,029.30   $1,029.40