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 $207.56   4.261%   $216.4041   $216.40   $216.40   $216.40  
  Purchase #2 $22.40   9.615%   $24.5538   $24.55   $24.55   $24.60  
  Purchase #3 $135.71   11.111%   $150.7887   $150.79   $150.80   $150.80  
  Purchase #4 $217.25   8.770%   $236.3028   $236.30   $236.30   $236.30  
  Purchase #5 $124.59   9.691%   $136.664   $136.66   $136.65   $136.70  
  Purchase #6 $211.81   6.562%   $225.709   $225.71   $225.70   $225.70  
  Purchase #7 $210.58   12.337%   $236.5593   $236.56   $236.55   $236.60  
  7 purchase totals = $1,129.90       $1,226.9817   $1,226.97   $1,226.95   $1,227.10