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 $38.72   11.485%   $43.167   $43.17   $43.15   $43.20  
  Purchase #2 $108.79   9.215%   $118.815   $118.82   $118.80   $118.80  
  Purchase #3 $249.59   11.814%   $279.0766   $279.08   $279.10   $279.10  
  Purchase #4 $95.56   9.258%   $104.4069   $104.41   $104.40   $104.40  
  Purchase #5 $207.76   5.442%   $219.0663   $219.07   $219.05   $219.10  
  Purchase #6 $67.43   3.438%   $69.7482   $69.75   $69.75   $69.70  
  Purchase #7 $59.43   7.160%   $63.6852   $63.69   $63.70   $63.70  
  7 purchase totals = $827.28       $897.9652   $897.99   $897.95   $898.00