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 $55.51   7.395%   $59.615   $59.62   $59.60   $59.60  
  Purchase #2 $195.30   3.212%   $201.573   $201.57   $201.55   $201.60  
  Purchase #3 $131.42   12.607%   $147.9881   $147.99   $148.00   $148.00  
  Purchase #4 $39.95   3.498%   $41.3475   $41.35   $41.35   $41.30  
  Purchase #5 $119.57   13.758%   $136.0204   $136.02   $136.00   $136.00  
  Purchase #6 $66.58   4.461%   $69.5501   $69.55   $69.55   $69.60  
  Purchase #7 $237.31   4.145%   $247.1465   $247.15   $247.15   $247.10  
  7 purchase totals = $845.64       $903.2406   $903.25   $903.20   $903.20