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 $91.94   10.678%   $101.7574   $101.76   $101.75   $101.80  
  Purchase #2 $126.63   12.644%   $142.6411   $142.64   $142.65   $142.60  
  Purchase #3 $107.48   7.789%   $115.8516   $115.85   $115.85   $115.90  
  Purchase #4 $175.26   6.227%   $186.1734   $186.17   $186.15   $186.20  
  Purchase #5 $104.64   8.721%   $113.7657   $113.77   $113.75   $113.80  
  Purchase #6 $122.32   12.472%   $137.5758   $137.58   $137.60   $137.60  
  Purchase #7 $147.43   3.615%   $152.7596   $152.76   $152.75   $152.80  
  7 purchase totals = $875.70       $950.5246   $950.53   $950.50   $950.70