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 $229.42   13.522%   $260.4422   $260.44   $260.45   $260.40  
  Purchase #2 $192.42   6.808%   $205.52   $205.52   $205.50   $205.50  
  Purchase #3 $25.72   6.626%   $27.4242   $27.42   $27.40   $27.40  
  Purchase #4 $124.31   11.632%   $138.7697   $138.77   $138.75   $138.80  
  Purchase #5 $149.47   3.611%   $154.8674   $154.87   $154.85   $154.90  
  Purchase #6 $65.95   11.322%   $73.4169   $73.42   $73.40   $73.40  
  Purchase #7 $192.48   12.376%   $216.3013   $216.30   $216.30   $216.30  
  7 purchase totals = $979.77       $1,076.7417   $1,076.74   $1,076.65   $1,076.70