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 $193.91   5.739%   $205.0385   $205.04   $205.05   $205.00  
  Purchase #2 $52.95   13.529%   $60.1136   $60.11   $60.10   $60.10  
  Purchase #3 $216.38   7.376%   $232.3402   $232.34   $232.35   $232.30  
  Purchase #4 $245.36   10.156%   $270.2788   $270.28   $270.30   $270.30  
  Purchase #5 $129.84   3.230%   $134.0338   $134.03   $134.05   $134.00  
  Purchase #6 $163.86   11.567%   $182.8137   $182.81   $182.80   $182.80  
  Purchase #7 $27.29   6.310%   $29.012   $29.01   $29.00   $29.00  
  7 purchase totals = $1,029.59       $1,113.6306   $1,113.62   $1,113.65   $1,113.50