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 $100.55   11.803%   $112.4179   $112.42   $112.40   $112.40  
  Purchase #2 $230.35   7.840%   $248.4094   $248.41   $248.40   $248.40  
  Purchase #3 $19.87   8.305%   $21.5202   $21.52   $21.50   $21.50  
  Purchase #4 $72.29   12.668%   $81.4477   $81.45   $81.45   $81.40  
  Purchase #5 $126.49   5.292%   $133.1839   $133.18   $133.20   $133.20  
  Purchase #6 $242.77   12.119%   $272.1913   $272.19   $272.20   $272.20  
  Purchase #7 $129.77   8.330%   $140.5798   $140.58   $140.60   $140.60  
  7 purchase totals = $922.09       $1,009.7502   $1,009.75   $1,009.75   $1,009.70