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 $30.80   4.282%   $32.1189   $32.12   $32.10   $32.10  
  Purchase #2 $210.45   12.141%   $236.0007   $236.00   $236.00   $236.00  
  Purchase #3 $104.39   8.769%   $113.544   $113.54   $113.55   $113.50  
  Purchase #4 $193.27   9.423%   $211.4818   $211.48   $211.50   $211.50  
  Purchase #5 $80.46   10.463%   $88.8785   $88.88   $88.90   $88.90  
  Purchase #6 $211.78   7.171%   $226.9667   $226.97   $226.95   $227.00  
  Purchase #7 $243.39   6.664%   $259.6095   $259.61   $259.60   $259.60  
  7 purchase totals = $1,074.54       $1,168.6001   $1,168.60   $1,168.60   $1,168.60