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 $208.25   6.463%   $221.7092   $221.71   $221.70   $221.70  
  Purchase #2 $54.77   6.697%   $58.4379   $58.44   $58.45   $58.40  
  Purchase #3 $215.82   3.124%   $222.5622   $222.56   $222.55   $222.60  
  Purchase #4 $209.90   4.355%   $219.0411   $219.04   $219.05   $219.00  
  Purchase #5 $211.99   6.359%   $225.4704   $225.47   $225.45   $225.50  
  Purchase #6 $153.59   9.132%   $167.6158   $167.62   $167.60   $167.60  
  Purchase #7 $194.75   8.320%   $210.9532   $210.95   $210.95   $211.00  
  7 purchase totals = $1,249.07       $1,325.7898   $1,325.79   $1,325.75   $1,325.80