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 $98.97   13.761%   $112.5893   $112.59   $112.60   $112.60  
  Purchase #2 $38.96   9.827%   $42.7886   $42.79   $42.80   $42.80  
  Purchase #3 $167.88   6.299%   $178.4548   $178.45   $178.45   $178.50  
  Purchase #4 $241.60   5.129%   $253.9917   $253.99   $254.00   $254.00  
  Purchase #5 $198.79   8.688%   $216.0609   $216.06   $216.05   $216.10  
  Purchase #6 $163.95   4.713%   $171.677   $171.68   $171.70   $171.70  
  Purchase #7 $181.96   10.655%   $201.3478   $201.35   $201.35   $201.30  
  7 purchase totals = $1,092.11       $1,176.9101   $1,176.91   $1,176.95   $1,177.00