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 $192.84   7.309%   $206.9347   $206.93   $206.95   $206.90  
  Purchase #2 $178.35   6.729%   $190.3512   $190.35   $190.35   $190.40  
  Purchase #3 $61.89   6.794%   $66.0948   $66.09   $66.10   $66.10  
  Purchase #4 $231.99   7.219%   $248.7374   $248.74   $248.75   $248.70  
  Purchase #5 $31.93   13.309%   $36.1796   $36.18   $36.20   $36.20  
  Purchase #6 $68.70   3.366%   $71.0124   $71.01   $71.00   $71.00  
  Purchase #7 $189.63   11.328%   $211.1113   $211.11   $211.10   $211.10  
  7 purchase totals = $955.33       $1,030.4214   $1,030.41   $1,030.45   $1,030.40