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 $223.85   13.249%   $253.5079   $253.51   $253.50   $253.50  
  Purchase #2 $87.35   6.127%   $92.7019   $92.70   $92.70   $92.70  
  Purchase #3 $211.83   10.142%   $233.3138   $233.31   $233.30   $233.30  
  Purchase #4 $227.66   7.827%   $245.4789   $245.48   $245.50   $245.50  
  Purchase #5 $232.92   6.325%   $247.6522   $247.65   $247.65   $247.70  
  Purchase #6 $60.32   5.397%   $63.5755   $63.58   $63.60   $63.60  
  Purchase #7 $71.73   11.629%   $80.0715   $80.07   $80.05   $80.10  
  7 purchase totals = $1,115.66       $1,216.3017   $1,216.30   $1,216.30   $1,216.40