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 $237.94   11.541%   $265.4007   $265.40   $265.40   $265.40  
  Purchase #2 $152.44   3.416%   $157.6474   $157.65   $157.65   $157.60  
  Purchase #3 $74.88   5.528%   $79.0194   $79.02   $79.00   $79.00  
  Purchase #4 $116.58   11.621%   $130.1278   $130.13   $130.15   $130.10  
  Purchase #5 $182.27   12.487%   $205.0301   $205.03   $205.05   $205.00  
  Purchase #6 $89.76   6.123%   $95.256   $95.26   $95.25   $95.30  
  Purchase #7 $165.37   3.309%   $170.8421   $170.84   $170.85   $170.80  
  7 purchase totals = $1,019.24       $1,103.3235   $1,103.33   $1,103.35   $1,103.20