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 $103.26   12.562%   $116.2315   $116.23   $116.25   $116.20  
  Purchase #2 $241.74   3.643%   $250.5466   $250.55   $250.55   $250.50  
  Purchase #3 $248.37   13.518%   $281.9447   $281.94   $281.95   $281.90  
  Purchase #4 $106.81   10.588%   $118.119   $118.12   $118.10   $118.10  
  Purchase #5 $160.68   10.202%   $177.0726   $177.07   $177.05   $177.10  
  Purchase #6 $211.44   6.323%   $224.8094   $224.81   $224.80   $224.80  
  Purchase #7 $129.54   3.231%   $133.7254   $133.73   $133.75   $133.70  
  7 purchase totals = $1,201.84       $1,302.4492   $1,302.45   $1,302.45   $1,302.30