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 $196.38   6.309%   $208.7696   $208.77   $208.75   $208.80  
  Purchase #2 $60.48   8.636%   $65.7031   $65.70   $65.70   $65.70  
  Purchase #3 $245.70   3.423%   $254.1103   $254.11   $254.10   $254.10  
  Purchase #4 $195.31   3.720%   $202.5755   $202.58   $202.60   $202.60  
  Purchase #5 $147.52   6.586%   $157.2357   $157.24   $157.25   $157.20  
  Purchase #6 $193.59   4.765%   $202.8146   $202.81   $202.80   $202.80  
  Purchase #7 $8.68   11.229%   $9.6547   $9.65   $9.65   $9.70  
  7 purchase totals = $1,047.66       $1,100.8635   $1,100.86   $1,100.85   $1,100.90