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 $226.53   4.548%   $236.8326   $236.83   $236.85   $236.80  
  Purchase #2 $179.72   11.244%   $199.9277   $199.93   $199.95   $199.90  
  Purchase #3 $62.80   7.170%   $67.3028   $67.30   $67.30   $67.30  
  Purchase #4 $213.72   3.745%   $221.7238   $221.72   $221.70   $221.70  
  Purchase #5 $7.72   10.481%   $8.5291   $8.53   $8.55   $8.50  
  Purchase #6 $61.36   3.635%   $63.5904   $63.59   $63.60   $63.60  
  Purchase #7 $238.81   12.306%   $268.198   $268.20   $268.20   $268.20  
  7 purchase totals = $990.66       $1,066.1044   $1,066.10   $1,066.15   $1,066.00