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 $176.92   11.825%   $197.8408   $197.84   $197.85   $197.80  
  Purchase #2 $30.89   13.305%   $34.9999   $35.00   $35.00   $35.00  
  Purchase #3 $117.99   6.440%   $125.5886   $125.59   $125.60   $125.60  
  Purchase #4 $175.40   9.709%   $192.4296   $192.43   $192.45   $192.40  
  Purchase #5 $238.81   11.398%   $266.0296   $266.03   $266.05   $266.00  
  Purchase #6 $184.68   9.553%   $202.3225   $202.32   $202.30   $202.30  
  Purchase #7 $37.69   5.300%   $39.6876   $39.69   $39.70   $39.70  
  7 purchase totals = $962.38       $1,058.8986   $1,058.90   $1,058.95   $1,058.80