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 $66.52   8.766%   $72.3511   $72.35   $72.35   $72.40  
  Purchase #2 $174.39   12.217%   $195.6952   $195.70   $195.70   $195.70  
  Purchase #3 $214.62   5.487%   $226.3962   $226.40   $226.40   $226.40  
  Purchase #4 $242.59   13.154%   $274.5003   $274.50   $274.50   $274.50  
  Purchase #5 $15.55   8.415%   $16.8585   $16.86   $16.85   $16.90  
  Purchase #6 $167.58   6.765%   $178.9168   $178.92   $178.90   $178.90  
  Purchase #7 $147.71   7.465%   $158.7366   $158.74   $158.75   $158.70  
  7 purchase totals = $1,028.96       $1,123.4547   $1,123.47   $1,123.45   $1,123.50