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 $55.89   8.537%   $60.6613   $60.66   $60.65   $60.70  
  Purchase #2 $110.39   10.181%   $121.6288   $121.63   $121.65   $121.60  
  Purchase #3 $45.80   4.509%   $47.8651   $47.87   $47.85   $47.90  
  Purchase #4 $246.46   9.281%   $269.334   $269.33   $269.35   $269.30  
  Purchase #5 $223.67   4.203%   $233.0709   $233.07   $233.05   $233.10  
  Purchase #6 $229.67   7.547%   $247.0032   $247.00   $247.00   $247.00  
  Purchase #7 $249.98   6.650%   $266.6037   $266.60   $266.60   $266.60  
  7 purchase totals = $1,161.86       $1,246.1670   $1,246.16   $1,246.15   $1,246.20