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 $49.41   9.406%   $54.0575   $54.06   $54.05   $54.10  
  Purchase #2 $60.85   10.128%   $67.0129   $67.01   $67.00   $67.00  
  Purchase #3 $226.84   8.435%   $245.974   $245.97   $245.95   $246.00  
  Purchase #4 $230.61   5.843%   $244.0845   $244.08   $244.10   $244.10  
  Purchase #5 $142.49   8.538%   $154.6558   $154.66   $154.65   $154.70  
  Purchase #6 $249.33   10.706%   $276.0233   $276.02   $276.00   $276.00  
  Purchase #7 $208.46   6.346%   $221.6889   $221.69   $221.70   $221.70  
  7 purchase totals = $1,167.99       $1,263.4969   $1,263.49   $1,263.45   $1,263.60