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 $200.76   12.422%   $225.6984   $225.70   $225.70   $225.70  
  Purchase #2 $152.54   7.365%   $163.7746   $163.77   $163.75   $163.80  
  Purchase #3 $207.82   7.558%   $223.527   $223.53   $223.55   $223.50  
  Purchase #4 $123.31   12.734%   $139.0123   $139.01   $139.00   $139.00  
  Purchase #5 $223.55   11.676%   $249.6517   $249.65   $249.65   $249.70  
  Purchase #6 $156.46   5.595%   $165.2139   $165.21   $165.20   $165.20  
  Purchase #7 $88.44   8.381%   $95.8522   $95.85   $95.85   $95.90  
  7 purchase totals = $1,152.88       $1,262.7301   $1,262.72   $1,262.70   $1,262.80