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 $49.71   7.202%   $53.2901   $53.29   $53.30   $53.30  
  Purchase #2 $147.82   9.477%   $161.8289   $161.83   $161.85   $161.80  
  Purchase #3 $238.79   11.738%   $266.8192   $266.82   $266.80   $266.80  
  Purchase #4 $35.58   5.253%   $37.449   $37.45   $37.45   $37.40  
  Purchase #5 $240.92   5.575%   $254.3513   $254.35   $254.35   $254.40  
  Purchase #6 $187.44   5.298%   $197.3706   $197.37   $197.35   $197.40  
  Purchase #7 $215.96   4.777%   $226.2764   $226.28   $226.30   $226.30  
  7 purchase totals = $1,116.22       $1,197.3855   $1,197.39   $1,197.40   $1,197.40