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 $97.98   6.299%   $104.1518   $104.15   $104.15   $104.20  
  Purchase #2 $191.94   8.775%   $208.7827   $208.78   $208.80   $208.80  
  Purchase #3 $11.70   11.611%   $13.0585   $13.06   $13.05   $13.10  
  Purchase #4 $126.93   8.348%   $137.5261   $137.53   $137.55   $137.50  
  Purchase #5 $105.97   8.208%   $114.668   $114.67   $114.65   $114.70  
  Purchase #6 $208.96   13.454%   $237.0735   $237.07   $237.05   $237.10  
  Purchase #7 $212.75   10.749%   $235.6185   $235.62   $235.60   $235.60  
  7 purchase totals = $956.23       $1,050.8791   $1,050.88   $1,050.85   $1,051.00