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 $162.63   6.572%   $173.318   $173.32   $173.30   $173.30  
  Purchase #2 $5.81   10.792%   $6.437   $6.44   $6.45   $6.40  
  Purchase #3 $175.82   9.486%   $192.4983   $192.50   $192.50   $192.50  
  Purchase #4 $204.91   9.812%   $225.0158   $225.02   $225.00   $225.00  
  Purchase #5 $200.74   11.842%   $224.5116   $224.51   $224.50   $224.50  
  Purchase #6 $54.66   12.544%   $61.5166   $61.52   $61.50   $61.50  
  Purchase #7 $205.74   6.133%   $218.358   $218.36   $218.35   $218.40  
  7 purchase totals = $1,010.31       $1,101.6553   $1,101.67   $1,101.60   $1,101.60