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 $203.81   11.183%   $226.6021   $226.60   $226.60   $226.60  
  Purchase #2 $11.95   11.814%   $13.3618   $13.36   $13.35   $13.40  
  Purchase #3 $14.49   12.147%   $16.2501   $16.25   $16.25   $16.30  
  Purchase #4 $84.96   4.316%   $88.6269   $88.63   $88.65   $88.60  
  Purchase #5 $241.93   10.759%   $267.9592   $267.96   $267.95   $268.00  
  Purchase #6 $73.65   6.350%   $78.3268   $78.33   $78.35   $78.30  
  Purchase #7 $111.43   3.637%   $115.4827   $115.48   $115.50   $115.50  
  7 purchase totals = $742.22       $806.6096   $806.61   $806.65   $806.70