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 $175.47   11.144%   $195.0244   $195.02   $195.00   $195.00  
  Purchase #2 $41.53   7.336%   $44.5766   $44.58   $44.60   $44.60  
  Purchase #3 $213.98   7.231%   $229.4529   $229.45   $229.45   $229.50  
  Purchase #4 $61.41   10.330%   $67.7537   $67.75   $67.75   $67.80  
  Purchase #5 $167.66   8.200%   $181.4081   $181.41   $181.40   $181.40  
  Purchase #6 $28.72   5.661%   $30.3458   $30.35   $30.35   $30.30  
  Purchase #7 $229.33   12.227%   $257.3702   $257.37   $257.35   $257.40  
  7 purchase totals = $918.10       $1,005.9317   $1,005.93   $1,005.90   $1,006.00