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 $145.84   13.274%   $165.1988   $165.20   $165.20   $165.20  
  Purchase #2 $124.48   11.618%   $138.9421   $138.94   $138.95   $138.90  
  Purchase #3 $216.45   11.694%   $241.7617   $241.76   $241.75   $241.80  
  Purchase #4 $50.70   13.292%   $57.439   $57.44   $57.45   $57.40  
  Purchase #5 $44.26   11.142%   $49.1914   $49.19   $49.20   $49.20  
  Purchase #6 $234.94   7.588%   $252.7672   $252.77   $252.75   $252.80  
  Purchase #7 $102.76   10.810%   $113.8684   $113.87   $113.85   $113.90  
  7 purchase totals = $919.43       $1,019.1686   $1,019.17   $1,019.15   $1,019.20