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 $55.90   7.649%   $60.1758   $60.18   $60.20   $60.20  
  Purchase #2 $191.66   12.653%   $215.9107   $215.91   $215.90   $215.90  
  Purchase #3 $85.27   7.378%   $91.5612   $91.56   $91.55   $91.60  
  Purchase #4 $119.52   10.652%   $132.2513   $132.25   $132.25   $132.30  
  Purchase #5 $217.69   4.195%   $226.8221   $226.82   $226.80   $226.80  
  Purchase #6 $196.73   13.576%   $223.4381   $223.44   $223.45   $223.40  
  Purchase #7 $123.97   8.502%   $134.5099   $134.51   $134.50   $134.50  
  7 purchase totals = $990.74       $1,084.6691   $1,084.67   $1,084.65   $1,084.70