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 $248.96   6.679%   $265.588   $265.59   $265.60   $265.60  
  Purchase #2 $136.77   7.256%   $146.694   $146.69   $146.70   $146.70  
  Purchase #3 $199.94   3.444%   $206.8259   $206.83   $206.85   $206.80  
  Purchase #4 $96.89   5.496%   $102.2151   $102.22   $102.20   $102.20  
  Purchase #5 $200.99   12.128%   $225.3661   $225.37   $225.35   $225.40  
  Purchase #6 $17.98   11.306%   $20.0128   $20.01   $20.00   $20.00  
  Purchase #7 $60.75   8.597%   $65.9727   $65.97   $65.95   $66.00  
  7 purchase totals = $962.28       $1,032.6746   $1,032.68   $1,032.65   $1,032.70