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 $227.86   8.248%   $246.6539   $246.65   $246.65   $246.70  
  Purchase #2 $134.84   10.476%   $148.9658   $148.97   $148.95   $149.00  
  Purchase #3 $52.53   5.627%   $55.4859   $55.49   $55.50   $55.50  
  Purchase #4 $204.61   8.646%   $222.3006   $222.30   $222.30   $222.30  
  Purchase #5 $224.55   13.351%   $254.5297   $254.53   $254.55   $254.50  
  Purchase #6 $124.61   6.503%   $132.7134   $132.71   $132.70   $132.70  
  Purchase #7 $148.81   3.400%   $153.8695   $153.87   $153.85   $153.90  
  7 purchase totals = $1,117.81       $1,214.5188   $1,214.52   $1,214.50   $1,214.60