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 $49.84   5.693%   $52.6774   $52.68   $52.70   $52.70  
  Purchase #2 $201.29   10.434%   $222.2926   $222.29   $222.30   $222.30  
  Purchase #3 $55.33   6.393%   $58.8672   $58.87   $58.85   $58.90  
  Purchase #4 $245.74   9.555%   $269.2205   $269.22   $269.20   $269.20  
  Purchase #5 $40.51   8.754%   $44.0562   $44.06   $44.05   $44.10  
  Purchase #6 $33.57   10.388%   $37.0573   $37.06   $37.05   $37.10  
  Purchase #7 $49.29   13.865%   $56.1241   $56.12   $56.10   $56.10  
  7 purchase totals = $675.57       $740.2953   $740.30   $740.25   $740.40