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 $47.74   9.619%   $52.3321   $52.33   $52.35   $52.30  
  Purchase #2 $192.68   8.438%   $208.9383   $208.94   $208.95   $208.90  
  Purchase #3 $67.95   13.490%   $77.1165   $77.12   $77.10   $77.10  
  Purchase #4 $189.86   7.786%   $204.6425   $204.64   $204.65   $204.60  
  Purchase #5 $169.61   11.747%   $189.5341   $189.53   $189.55   $189.50  
  Purchase #6 $184.41   13.272%   $208.8849   $208.88   $208.90   $208.90  
  Purchase #7 $63.31   10.147%   $69.7341   $69.73   $69.75   $69.70  
  7 purchase totals = $915.56       $1,011.1825   $1,011.17   $1,011.25   $1,011.00