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 $11.63   8.172%   $12.5804   $12.58   $12.60   $12.60  
  Purchase #2 $196.52   10.208%   $216.5808   $216.58   $216.60   $216.60  
  Purchase #3 $65.73   4.277%   $68.5413   $68.54   $68.55   $68.50  
  Purchase #4 $20.69   5.379%   $21.8029   $21.80   $21.80   $21.80  
  Purchase #5 $204.65   4.190%   $213.2248   $213.22   $213.20   $213.20  
  Purchase #6 $182.30   11.385%   $203.0549   $203.05   $203.05   $203.10  
  Purchase #7 $57.67   4.365%   $60.1873   $60.19   $60.20   $60.20  
  7 purchase totals = $739.19       $795.9724   $795.96   $796.00   $796.00