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 $88.72   8.289%   $96.074   $96.07   $96.05   $96.10  
  Purchase #2 $205.84   9.107%   $224.5858   $224.59   $224.60   $224.60  
  Purchase #3 $42.85   6.255%   $45.5303   $45.53   $45.55   $45.50  
  Purchase #4 $17.30   13.219%   $19.5869   $19.59   $19.60   $19.60  
  Purchase #5 $44.68   13.608%   $50.7601   $50.76   $50.75   $50.80  
  Purchase #6 $203.89   6.332%   $216.8003   $216.80   $216.80   $216.80  
  Purchase #7 $38.76   11.737%   $43.3093   $43.31   $43.30   $43.30  
  7 purchase totals = $642.04       $696.6467   $696.65   $696.65   $696.70