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 $156.68   4.796%   $164.1944   $164.19   $164.20   $164.20  
  Purchase #2 $97.94   8.777%   $106.5362   $106.54   $106.55   $106.50  
  Purchase #3 $248.72   11.437%   $277.1661   $277.17   $277.15   $277.20  
  Purchase #4 $182.79   4.811%   $191.584   $191.58   $191.60   $191.60  
  Purchase #5 $49.69   5.564%   $52.4548   $52.45   $52.45   $52.50  
  Purchase #6 $210.31   12.178%   $235.9216   $235.92   $235.90   $235.90  
  Purchase #7 $209.67   6.660%   $223.634   $223.63   $223.65   $223.60  
  7 purchase totals = $1,155.80       $1,251.4911   $1,251.48   $1,251.50   $1,251.50