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 $182.91   3.482%   $189.2789   $189.28   $189.30   $189.30  
  Purchase #2 $85.54   10.820%   $94.7954   $94.80   $94.80   $94.80  
  Purchase #3 $110.65   5.135%   $116.3319   $116.33   $116.35   $116.30  
  Purchase #4 $44.97   6.528%   $47.9056   $47.91   $47.90   $47.90  
  Purchase #5 $232.29   11.855%   $259.828   $259.83   $259.85   $259.80  
  Purchase #6 $60.83   4.769%   $63.731   $63.73   $63.75   $63.70  
  Purchase #7 $237.74   11.297%   $264.5975   $264.60   $264.60   $264.60  
  7 purchase totals = $954.93       $1,036.4683   $1,036.48   $1,036.55   $1,036.40