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 $62.29   13.399%   $70.6362   $70.64   $70.65   $70.60  
  Purchase #2 $57.72   4.528%   $60.3336   $60.33   $60.35   $60.30  
  Purchase #3 $75.62   6.703%   $80.6888   $80.69   $80.70   $80.70  
  Purchase #4 $190.89   9.403%   $208.8394   $208.84   $208.85   $208.80  
  Purchase #5 $82.33   11.432%   $91.742   $91.74   $91.75   $91.70  
  Purchase #6 $16.74   9.601%   $18.3472   $18.35   $18.35   $18.30  
  Purchase #7 $168.26   5.793%   $178.0073   $178.01   $178.00   $178.00  
  7 purchase totals = $653.85       $708.5945   $708.60   $708.65   $708.40