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 $212.87   8.794%   $231.5898   $231.59   $231.60   $231.60  
  Purchase #2 $144.91   6.868%   $154.8624   $154.86   $154.85   $154.90  
  Purchase #3 $44.28   5.786%   $46.842   $46.84   $46.85   $46.80  
  Purchase #4 $32.50   6.686%   $34.673   $34.67   $34.65   $34.70  
  Purchase #5 $9.32   4.582%   $9.747   $9.75   $9.75   $9.70  
  Purchase #6 $210.60   12.657%   $237.2556   $237.26   $237.25   $237.30  
  Purchase #7 $218.28   9.473%   $238.9577   $238.96   $238.95   $239.00  
  7 purchase totals = $872.76       $953.9275   $953.93   $953.90   $954.00