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 $64.83   10.702%   $71.7681   $71.77   $71.75   $71.80  
  Purchase #2 $66.72   9.640%   $73.1518   $73.15   $73.15   $73.20  
  Purchase #3 $100.90   13.389%   $114.4095   $114.41   $114.40   $114.40  
  Purchase #4 $184.40   5.851%   $195.1892   $195.19   $195.20   $195.20  
  Purchase #5 $74.92   3.855%   $77.8082   $77.81   $77.80   $77.80  
  Purchase #6 $181.52   11.688%   $202.7361   $202.74   $202.75   $202.70  
  Purchase #7 $16.82   9.652%   $18.4435   $18.44   $18.45   $18.40  
  7 purchase totals = $690.11       $753.5064   $753.51   $753.50   $753.50