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 $212.33   13.666%   $241.347   $241.35   $241.35   $241.30  
  Purchase #2 $69.66   11.309%   $77.5378   $77.54   $77.55   $77.50  
  Purchase #3 $41.57   5.115%   $43.6963   $43.70   $43.70   $43.70  
  Purchase #4 $44.45   12.318%   $49.9254   $49.93   $49.95   $49.90  
  Purchase #5 $244.50   8.275%   $264.7324   $264.73   $264.75   $264.70  
  Purchase #6 $55.39   10.449%   $61.1777   $61.18   $61.20   $61.20  
  Purchase #7 $82.72   13.775%   $94.1147   $94.11   $94.10   $94.10  
  7 purchase totals = $750.62       $832.5313   $832.54   $832.60   $832.40