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 $83.71   11.451%   $93.2956   $93.30   $93.30   $93.30  
  Purchase #2 $224.85   10.762%   $249.0484   $249.05   $249.05   $249.00  
  Purchase #3 $163.27   12.232%   $183.2412   $183.24   $183.25   $183.20  
  Purchase #4 $49.53   5.302%   $52.1561   $52.16   $52.15   $52.20  
  Purchase #5 $52.28   11.869%   $58.4851   $58.49   $58.50   $58.50  
  Purchase #6 $181.53   12.620%   $204.4391   $204.44   $204.45   $204.40  
  Purchase #7 $233.66   12.619%   $263.1456   $263.15   $263.15   $263.10  
  7 purchase totals = $988.83       $1,103.8111   $1,103.83   $1,103.85   $1,103.70