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 $60.37   8.869%   $65.7242   $65.72   $65.70   $65.70  
  Purchase #2 $203.48   5.142%   $213.9429   $213.94   $213.95   $213.90  
  Purchase #3 $179.77   7.338%   $192.9615   $192.96   $192.95   $193.00  
  Purchase #4 $30.40   7.439%   $32.6615   $32.66   $32.65   $32.70  
  Purchase #5 $157.86   7.643%   $169.9252   $169.93   $169.95   $169.90  
  Purchase #6 $210.90   3.403%   $218.0769   $218.08   $218.10   $218.10  
  Purchase #7 $28.47   4.873%   $29.8573   $29.86   $29.85   $29.90  
  7 purchase totals = $871.25       $923.1495   $923.15   $923.15   $923.20