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 $232.61   9.558%   $254.8429   $254.84   $254.85   $254.80  
  Purchase #2 $89.74   3.243%   $92.6503   $92.65   $92.65   $92.70  
  Purchase #3 $100.29   6.374%   $106.6825   $106.68   $106.70   $106.70  
  Purchase #4 $115.87   13.278%   $131.2552   $131.26   $131.25   $131.30  
  Purchase #5 $36.69   7.134%   $39.3075   $39.31   $39.30   $39.30  
  Purchase #6 $158.41   11.359%   $176.4038   $176.40   $176.40   $176.40  
  Purchase #7 $181.75   10.152%   $200.2013   $200.20   $200.20   $200.20  
  7 purchase totals = $915.36       $1,001.3435   $1,001.34   $1,001.35   $1,001.40