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 $193.74   12.565%   $218.0834   $218.08   $218.10   $218.10  
  Purchase #2 $217.76   8.217%   $235.6533   $235.65   $235.65   $235.70  
  Purchase #3 $74.60   4.683%   $78.0935   $78.09   $78.10   $78.10  
  Purchase #4 $43.39   5.121%   $45.612   $45.61   $45.60   $45.60  
  Purchase #5 $99.28   3.247%   $102.5036   $102.50   $102.50   $102.50  
  Purchase #6 $187.98   7.289%   $201.6819   $201.68   $201.70   $201.70  
  Purchase #7 $120.99   7.475%   $130.034   $130.03   $130.05   $130.00  
  7 purchase totals = $937.74       $1,011.6617   $1,011.64   $1,011.70   $1,011.70