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 $9.78   11.309%   $10.886   $10.89   $10.90   $10.90  
  Purchase #2 $185.53   13.182%   $209.9866   $209.99   $210.00   $210.00  
  Purchase #3 $208.78   3.596%   $216.2877   $216.29   $216.30   $216.30  
  Purchase #4 $54.68   12.729%   $61.6402   $61.64   $61.65   $61.60  
  Purchase #5 $219.35   5.446%   $231.2958   $231.30   $231.30   $231.30  
  Purchase #6 $25.75   10.481%   $28.4489   $28.45   $28.45   $28.40  
  Purchase #7 $79.30   11.658%   $88.5448   $88.54   $88.55   $88.50  
  7 purchase totals = $783.17       $847.0900   $847.10   $847.15   $847.00