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 $34.76   8.726%   $37.7932   $37.79   $37.80   $37.80  
  Purchase #2 $239.58   7.107%   $256.607   $256.61   $256.60   $256.60  
  Purchase #3 $227.42   11.533%   $253.6483   $253.65   $253.65   $253.60  
  Purchase #4 $23.42   9.847%   $25.7262   $25.73   $25.75   $25.70  
  Purchase #5 $18.30   12.419%   $20.5727   $20.57   $20.55   $20.60  
  Purchase #6 $226.69   9.358%   $247.9037   $247.90   $247.90   $247.90  
  Purchase #7 $204.33   7.857%   $220.3842   $220.38   $220.40   $220.40  
  7 purchase totals = $974.50       $1,062.6353   $1,062.63   $1,062.65   $1,062.60