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 $44.35   11.830%   $49.5966   $49.60   $49.60   $49.60  
  Purchase #2 $138.73   10.808%   $153.7239   $153.72   $153.70   $153.70  
  Purchase #3 $56.28   6.683%   $60.0412   $60.04   $60.05   $60.00  
  Purchase #4 $193.68   7.543%   $208.2893   $208.29   $208.30   $208.30  
  Purchase #5 $18.35   12.209%   $20.5904   $20.59   $20.60   $20.60  
  Purchase #6 $243.84   12.824%   $275.11   $275.11   $275.10   $275.10  
  Purchase #7 $212.91   13.607%   $241.8807   $241.88   $241.90   $241.90  
  7 purchase totals = $908.14       $1,009.2321   $1,009.23   $1,009.25   $1,009.20