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 $15.93   10.432%   $17.5918   $17.59   $17.60   $17.60  
  Purchase #2 $117.91   4.358%   $123.0485   $123.05   $123.05   $123.00  
  Purchase #3 $194.62   9.798%   $213.6889   $213.69   $213.70   $213.70  
  Purchase #4 $147.45   3.778%   $153.0207   $153.02   $153.00   $153.00  
  Purchase #5 $16.43   10.703%   $18.1885   $18.19   $18.20   $18.20  
  Purchase #6 $38.45   11.782%   $42.9802   $42.98   $43.00   $43.00  
  Purchase #7 $120.65   3.856%   $125.3023   $125.30   $125.30   $125.30  
  7 purchase totals = $651.44       $693.8209   $693.82   $693.85   $693.80