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 $155.93   13.111%   $176.374   $176.37   $176.35   $176.40  
  Purchase #2 $209.73   5.731%   $221.7496   $221.75   $221.75   $221.70  
  Purchase #3 $147.34   4.502%   $153.9732   $153.97   $153.95   $154.00  
  Purchase #4 $76.44   6.691%   $81.5546   $81.55   $81.55   $81.60  
  Purchase #5 $80.94   10.769%   $89.6564   $89.66   $89.65   $89.70  
  Purchase #6 $108.77   5.831%   $115.1124   $115.11   $115.10   $115.10  
  Purchase #7 $152.64   6.124%   $161.9877   $161.99   $162.00   $162.00  
  7 purchase totals = $931.79       $1,000.4079   $1,000.40   $1,000.35   $1,000.50