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 $87.80   9.851%   $96.4492   $96.45   $96.45   $96.40  
  Purchase #2 $250.98   3.112%   $258.7905   $258.79   $258.80   $258.80  
  Purchase #3 $163.94   7.783%   $176.6995   $176.70   $176.70   $176.70  
  Purchase #4 $147.92   11.452%   $164.8598   $164.86   $164.85   $164.90  
  Purchase #5 $24.94   5.426%   $26.2932   $26.29   $26.30   $26.30  
  Purchase #6 $59.91   13.612%   $68.0649   $68.06   $68.05   $68.10  
  Purchase #7 $39.64   3.407%   $40.9905   $40.99   $41.00   $41.00  
  7 purchase totals = $775.13       $832.1476   $832.14   $832.15   $832.20