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 $38.73   11.123%   $43.0379   $43.04   $43.05   $43.00  
  Purchase #2 $108.98   6.115%   $115.6441   $115.64   $115.65   $115.60  
  Purchase #3 $94.31   11.201%   $104.8737   $104.87   $104.85   $104.90  
  Purchase #4 $246.36   5.182%   $259.1264   $259.13   $259.15   $259.10  
  Purchase #5 $230.65   8.123%   $249.3857   $249.39   $249.40   $249.40  
  Purchase #6 $157.80   8.168%   $170.6891   $170.69   $170.70   $170.70  
  Purchase #7 $40.93   11.796%   $45.7581   $45.76   $45.75   $45.80  
  7 purchase totals = $917.76       $988.5150   $988.52   $988.55   $988.50