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 $242.30   7.331%   $260.063   $260.06   $260.05   $260.10  
  Purchase #2 $113.48   7.469%   $121.9558   $121.96   $121.95   $122.00  
  Purchase #3 $224.70   5.718%   $237.5483   $237.55   $237.55   $237.50  
  Purchase #4 $212.83   9.548%   $233.151   $233.15   $233.15   $233.20  
  Purchase #5 $5.78   11.462%   $6.4425   $6.44   $6.45   $6.40  
  Purchase #6 $224.34   3.533%   $232.2659   $232.27   $232.25   $232.30  
  Purchase #7 $87.95   5.575%   $92.8532   $92.85   $92.85   $92.90  
  7 purchase totals = $1,111.38       $1,184.2797   $1,184.28   $1,184.25   $1,184.40