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 $211.53   12.523%   $238.0199   $238.02   $238.00   $238.00  
  Purchase #2 $74.41   10.851%   $82.4842   $82.48   $82.50   $82.50  
  Purchase #3 $120.59   13.446%   $136.8045   $136.80   $136.80   $136.80  
  Purchase #4 $150.65   4.413%   $157.2982   $157.30   $157.30   $157.30  
  Purchase #5 $177.55   12.286%   $199.3638   $199.36   $199.35   $199.40  
  Purchase #6 $64.49   5.646%   $68.1311   $68.13   $68.15   $68.10  
  Purchase #7 $232.63   8.861%   $253.2433   $253.24   $253.25   $253.20  
  7 purchase totals = $1,031.85       $1,135.3450   $1,135.33   $1,135.35   $1,135.30