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 $241.36   3.853%   $250.6596   $250.66   $250.65   $250.70  
  Purchase #2 $60.41   13.817%   $68.7568   $68.76   $68.75   $68.80  
  Purchase #3 $113.95   3.188%   $117.5827   $117.58   $117.60   $117.60  
  Purchase #4 $182.64   3.529%   $189.0854   $189.09   $189.10   $189.10  
  Purchase #5 $234.94   4.400%   $245.2774   $245.28   $245.30   $245.30  
  Purchase #6 $224.40   9.531%   $245.7876   $245.79   $245.80   $245.80  
  Purchase #7 $145.34   3.132%   $149.892   $149.89   $149.90   $149.90  
  7 purchase totals = $1,203.04       $1,267.0415   $1,267.05   $1,267.10   $1,267.20