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 $245.29   9.370%   $268.2737   $268.27   $268.25   $268.30  
  Purchase #2 $61.58   13.176%   $69.6938   $69.69   $69.70   $69.70  
  Purchase #3 $85.78   4.146%   $89.3364   $89.34   $89.35   $89.30  
  Purchase #4 $184.43   4.702%   $193.1019   $193.10   $193.10   $193.10  
  Purchase #5 $200.89   6.780%   $214.5103   $214.51   $214.50   $214.50  
  Purchase #6 $67.68   11.319%   $75.3407   $75.34   $75.35   $75.30  
  Purchase #7 $214.50   11.455%   $239.071   $239.07   $239.05   $239.10  
  7 purchase totals = $1,060.15       $1,149.3278   $1,149.32   $1,149.30   $1,149.30