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 $189.57   11.166%   $210.7374   $210.74   $210.75   $210.70  
  Purchase #2 $154.41   9.844%   $169.6101   $169.61   $169.60   $169.60  
  Purchase #3 $96.41   7.297%   $103.445   $103.45   $103.45   $103.40  
  Purchase #4 $131.85   5.569%   $139.1927   $139.19   $139.20   $139.20  
  Purchase #5 $250.71   9.624%   $274.8383   $274.84   $274.85   $274.80  
  Purchase #6 $66.55   10.643%   $73.6329   $73.63   $73.65   $73.60  
  Purchase #7 $27.27   10.565%   $30.1511   $30.15   $30.15   $30.20  
  7 purchase totals = $916.77       $1,001.6075   $1,001.61   $1,001.65   $1,001.50