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 $67.71   8.703%   $73.6028   $73.60   $73.60   $73.60  
  Purchase #2 $10.66   6.302%   $11.3318   $11.33   $11.35   $11.30  
  Purchase #3 $171.60   4.563%   $179.4301   $179.43   $179.45   $179.40  
  Purchase #4 $134.61   13.868%   $153.2777   $153.28   $153.30   $153.30  
  Purchase #5 $214.26   7.400%   $230.1152   $230.12   $230.10   $230.10  
  Purchase #6 $155.33   3.489%   $160.7495   $160.75   $160.75   $160.70  
  Purchase #7 $113.64   5.527%   $119.9209   $119.92   $119.90   $119.90  
  7 purchase totals = $867.81       $928.4280   $928.43   $928.45   $928.30