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 $89.68   3.479%   $92.8   $92.80   $92.80   $92.80  
  Purchase #2 $24.37   8.838%   $26.5238   $26.52   $26.50   $26.50  
  Purchase #3 $49.71   6.535%   $52.9585   $52.96   $52.95   $53.00  
  Purchase #4 $176.91   7.633%   $190.4135   $190.41   $190.40   $190.40  
  Purchase #5 $243.55   12.272%   $273.4385   $273.44   $273.45   $273.40  
  Purchase #6 $72.52   10.581%   $80.1933   $80.19   $80.20   $80.20  
  Purchase #7 $50.28   13.451%   $57.0432   $57.04   $57.05   $57.00  
  7 purchase totals = $707.02       $773.3708   $773.36   $773.35   $773.30