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 $66.55   11.439%   $74.1627   $74.16   $74.15   $74.20  
  Purchase #2 $154.54   13.378%   $175.2144   $175.21   $175.20   $175.20  
  Purchase #3 $122.99   11.661%   $137.3319   $137.33   $137.35   $137.30  
  Purchase #4 $132.37   11.139%   $147.1147   $147.11   $147.10   $147.10  
  Purchase #5 $238.53   6.670%   $254.44   $254.44   $254.45   $254.40  
  Purchase #6 $236.83   5.847%   $250.6775   $250.68   $250.70   $250.70  
  Purchase #7 $41.40   9.228%   $45.2204   $45.22   $45.20   $45.20  
  7 purchase totals = $993.21       $1,084.1616   $1,084.15   $1,084.15   $1,084.10