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 $217.78   3.271%   $224.9036   $224.90   $224.90   $224.90  
  Purchase #2 $57.89   6.366%   $61.5753   $61.58   $61.60   $61.60  
  Purchase #3 $53.56   9.351%   $58.5684   $58.57   $58.55   $58.60  
  Purchase #4 $134.42   6.751%   $143.4947   $143.49   $143.50   $143.50  
  Purchase #5 $226.92   4.251%   $236.5664   $236.57   $236.55   $236.60  
  Purchase #6 $25.72   6.727%   $27.4502   $27.45   $27.45   $27.50  
  Purchase #7 $245.79   11.535%   $274.1419   $274.14   $274.15   $274.10  
  7 purchase totals = $962.08       $1,026.7005   $1,026.70   $1,026.70   $1,026.80