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 $202.51   3.507%   $209.612   $209.61   $209.60   $209.60  
  Purchase #2 $107.49   10.385%   $118.6528   $118.65   $118.65   $118.70  
  Purchase #3 $46.30   11.579%   $51.6611   $51.66   $51.65   $51.70  
  Purchase #4 $210.80   13.771%   $239.8293   $239.83   $239.85   $239.80  
  Purchase #5 $98.67   8.217%   $106.7777   $106.78   $106.80   $106.80  
  Purchase #6 $153.79   7.379%   $165.1382   $165.14   $165.15   $165.10  
  Purchase #7 $139.41   13.761%   $158.5942   $158.59   $158.60   $158.60  
  7 purchase totals = $958.97       $1,050.2653   $1,050.26   $1,050.30   $1,050.30