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 $228.74   5.644%   $241.6501   $241.65   $241.65   $241.70  
  Purchase #2 $232.34   12.715%   $261.882   $261.88   $261.90   $261.90  
  Purchase #3 $54.36   13.509%   $61.7035   $61.70   $61.70   $61.70  
  Purchase #4 $163.44   10.813%   $181.1128   $181.11   $181.10   $181.10  
  Purchase #5 $31.38   9.643%   $34.406   $34.41   $34.40   $34.40  
  Purchase #6 $99.87   4.650%   $104.514   $104.51   $104.50   $104.50  
  Purchase #7 $187.26   10.591%   $207.0927   $207.09   $207.10   $207.10  
  7 purchase totals = $997.39       $1,092.3611   $1,092.35   $1,092.35   $1,092.40