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 $186.82   10.805%   $207.0059   $207.01   $207.00   $207.00  
  Purchase #2 $47.67   10.597%   $52.7216   $52.72   $52.70   $52.70  
  Purchase #3 $92.37   12.133%   $103.5773   $103.58   $103.60   $103.60  
  Purchase #4 $184.73   9.594%   $202.453   $202.45   $202.45   $202.50  
  Purchase #5 $35.79   8.193%   $38.7223   $38.72   $38.70   $38.70  
  Purchase #6 $208.65   8.387%   $226.1495   $226.15   $226.15   $226.10  
  Purchase #7 $192.78   10.444%   $212.9139   $212.91   $212.90   $212.90  
  7 purchase totals = $948.81       $1,043.5435   $1,043.54   $1,043.50   $1,043.50