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 $33.61   8.774%   $36.5589   $36.56   $36.55   $36.60  
  Purchase #2 $166.87   7.623%   $179.5905   $179.59   $179.60   $179.60  
  Purchase #3 $228.38   11.387%   $254.3856   $254.39   $254.40   $254.40  
  Purchase #4 $125.78   12.453%   $141.4434   $141.44   $141.45   $141.40  
  Purchase #5 $170.51   3.334%   $176.1948   $176.19   $176.20   $176.20  
  Purchase #6 $192.94   11.760%   $215.6297   $215.63   $215.65   $215.60  
  Purchase #7 $27.45   5.640%   $28.9982   $29.00   $29.00   $29.00  
  7 purchase totals = $945.54       $1,032.8011   $1,032.80   $1,032.85   $1,032.80