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 $116.97   8.535%   $126.9534   $126.95   $126.95   $127.00  
  Purchase #2 $127.33   8.868%   $138.6216   $138.62   $138.60   $138.60  
  Purchase #3 $56.39   3.441%   $58.3304   $58.33   $58.35   $58.30  
  Purchase #4 $142.78   5.790%   $151.047   $151.05   $151.05   $151.00  
  Purchase #5 $172.98   9.618%   $189.6172   $189.62   $189.60   $189.60  
  Purchase #6 $241.54   9.523%   $264.5419   $264.54   $264.55   $264.50  
  Purchase #7 $233.45   6.766%   $249.2452   $249.25   $249.25   $249.20  
  7 purchase totals = $1,091.44       $1,178.3567   $1,178.36   $1,178.35   $1,178.20