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 $78.83   5.494%   $83.1609   $83.16   $83.15   $83.20  
  Purchase #2 $99.98   5.716%   $105.6949   $105.69   $105.70   $105.70  
  Purchase #3 $94.86   5.286%   $99.8743   $99.87   $99.85   $99.90  
  Purchase #4 $109.62   6.402%   $116.6379   $116.64   $116.65   $116.60  
  Purchase #5 $57.64   8.586%   $62.589   $62.59   $62.60   $62.60  
  Purchase #6 $203.91   10.246%   $224.8026   $224.80   $224.80   $224.80  
  Purchase #7 $178.37   10.324%   $196.7849   $196.78   $196.80   $196.80  
  7 purchase totals = $823.21       $889.5445   $889.53   $889.55   $889.60