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 $94.43   7.610%   $101.6161   $101.62   $101.60   $101.60  
  Purchase #2 $77.85   11.333%   $86.6727   $86.67   $86.65   $86.70  
  Purchase #3 $119.59   7.378%   $128.4134   $128.41   $128.40   $128.40  
  Purchase #4 $157.74   7.691%   $169.8718   $169.87   $169.85   $169.90  
  Purchase #5 $112.82   11.323%   $125.5946   $125.59   $125.60   $125.60  
  Purchase #6 $108.82   9.428%   $119.0795   $119.08   $119.10   $119.10  
  Purchase #7 $160.63   8.149%   $173.7197   $173.72   $173.70   $173.70  
  7 purchase totals = $831.88       $904.9678   $904.96   $904.90   $905.00