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 $205.39   11.378%   $228.7593   $228.76   $228.75   $228.80  
  Purchase #2 $57.59   10.782%   $63.7994   $63.80   $63.80   $63.80  
  Purchase #3 $180.41   5.481%   $190.2983   $190.30   $190.30   $190.30  
  Purchase #4 $103.93   3.384%   $107.447   $107.45   $107.45   $107.40  
  Purchase #5 $175.65   5.394%   $185.1246   $185.12   $185.10   $185.10  
  Purchase #6 $5.61   11.819%   $6.273   $6.27   $6.25   $6.30  
  Purchase #7 $247.40   8.494%   $268.4142   $268.41   $268.40   $268.40  
  7 purchase totals = $975.98       $1,050.1158   $1,050.11   $1,050.05   $1,050.10