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 $55.94   8.510%   $60.7005   $60.70   $60.70   $60.70  
  Purchase #2 $49.85   6.643%   $53.1615   $53.16   $53.15   $53.20  
  Purchase #3 $88.27   5.771%   $93.3641   $93.36   $93.35   $93.40  
  Purchase #4 $131.92   7.151%   $141.3536   $141.35   $141.35   $141.40  
  Purchase #5 $178.61   11.635%   $199.3913   $199.39   $199.40   $199.40  
  Purchase #6 $179.42   12.579%   $201.9892   $201.99   $202.00   $202.00  
  Purchase #7 $138.35   6.727%   $147.6568   $147.66   $147.65   $147.70  
  7 purchase totals = $822.36       $897.6170   $897.61   $897.60   $897.80