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 $55.93   12.182%   $62.7434   $62.74   $62.75   $62.70  
  Purchase #2 $188.40   7.143%   $201.8574   $201.86   $201.85   $201.90  
  Purchase #3 $178.44   4.637%   $186.7143   $186.71   $186.70   $186.70  
  Purchase #4 $206.29   9.812%   $226.5312   $226.53   $226.55   $226.50  
  Purchase #5 $43.34   5.263%   $45.621   $45.62   $45.60   $45.60  
  Purchase #6 $245.98   8.248%   $266.2684   $266.27   $266.25   $266.30  
  Purchase #7 $101.26   7.794%   $109.1522   $109.15   $109.15   $109.20  
  7 purchase totals = $1,019.64       $1,098.8879   $1,098.88   $1,098.85   $1,098.90