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 $153.94   8.487%   $167.0049   $167.00   $167.00   $167.00  
  Purchase #2 $192.36   12.450%   $216.3088   $216.31   $216.30   $216.30  
  Purchase #3 $247.74   8.820%   $269.5907   $269.59   $269.60   $269.60  
  Purchase #4 $62.46   13.775%   $71.0639   $71.06   $71.05   $71.10  
  Purchase #5 $64.73   12.161%   $72.6018   $72.60   $72.60   $72.60  
  Purchase #6 $206.85   11.249%   $230.1186   $230.12   $230.10   $230.10  
  Purchase #7 $233.91   11.829%   $261.5792   $261.58   $261.60   $261.60  
  7 purchase totals = $1,161.99       $1,288.2679   $1,288.26   $1,288.25   $1,288.30