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 $40.59   11.701%   $45.3394   $45.34   $45.35   $45.30  
  Purchase #2 $226.71   3.719%   $235.1413   $235.14   $235.15   $235.10  
  Purchase #3 $81.45   13.371%   $92.3407   $92.34   $92.35   $92.30  
  Purchase #4 $176.44   8.400%   $191.261   $191.26   $191.25   $191.30  
  Purchase #5 $23.62   11.341%   $26.2987   $26.30   $26.30   $26.30  
  Purchase #6 $205.61   13.757%   $233.8958   $233.90   $233.90   $233.90  
  Purchase #7 $205.51   11.476%   $229.0943   $229.09   $229.10   $229.10  
  7 purchase totals = $959.93       $1,053.3712   $1,053.37   $1,053.40   $1,053.30