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 $214.60   6.517%   $228.5855   $228.59   $228.60   $228.60  
  Purchase #2 $20.36   11.783%   $22.759   $22.76   $22.75   $22.80  
  Purchase #3 $94.56   12.299%   $106.1899   $106.19   $106.20   $106.20  
  Purchase #4 $93.95   6.714%   $100.2578   $100.26   $100.25   $100.30  
  Purchase #5 $226.69   11.213%   $252.1087   $252.11   $252.10   $252.10  
  Purchase #6 $227.61   12.238%   $255.4649   $255.46   $255.45   $255.50  
  Purchase #7 $106.70   11.313%   $118.771   $118.77   $118.75   $118.80  
  7 purchase totals = $984.47       $1,084.1368   $1,084.14   $1,084.10   $1,084.30