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 $107.95   9.165%   $117.8436   $117.84   $117.85   $117.80  
  Purchase #2 $26.66   7.343%   $28.6176   $28.62   $28.60   $28.60  
  Purchase #3 $17.44   9.245%   $19.0523   $19.05   $19.05   $19.10  
  Purchase #4 $201.78   12.379%   $226.7583   $226.76   $226.75   $226.80  
  Purchase #5 $165.32   7.655%   $177.9752   $177.98   $178.00   $178.00  
  Purchase #6 $231.79   9.393%   $253.562   $253.56   $253.55   $253.60  
  Purchase #7 $175.61   11.435%   $195.691   $195.69   $195.70   $195.70  
  7 purchase totals = $926.55       $1,019.5000   $1,019.50   $1,019.50   $1,019.60