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 $92.82   3.571%   $96.1346   $96.13   $96.15   $96.10  
  Purchase #2 $173.57   9.430%   $189.9377   $189.94   $189.95   $189.90  
  Purchase #3 $71.86   12.561%   $80.8863   $80.89   $80.90   $80.90  
  Purchase #4 $95.67   8.397%   $103.7034   $103.70   $103.70   $103.70  
  Purchase #5 $52.77   3.467%   $54.5995   $54.60   $54.60   $54.60  
  Purchase #6 $193.56   4.202%   $201.6934   $201.69   $201.70   $201.70  
  Purchase #7 $179.45   4.787%   $188.0403   $188.04   $188.05   $188.00  
  7 purchase totals = $859.70       $914.9952   $914.99   $915.05   $914.90