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 $88.44   8.784%   $96.2086   $96.21   $96.20   $96.20  
  Purchase #2 $156.50   10.346%   $172.6915   $172.69   $172.70   $172.70  
  Purchase #3 $107.33   7.668%   $115.5601   $115.56   $115.55   $115.60  
  Purchase #4 $32.26   7.461%   $34.6669   $34.67   $34.65   $34.70  
  Purchase #5 $224.51   13.291%   $254.3496   $254.35   $254.35   $254.30  
  Purchase #6 $39.31   5.606%   $41.5137   $41.51   $41.50   $41.50  
  Purchase #7 $42.70   12.541%   $48.055   $48.06   $48.05   $48.10  
  7 purchase totals = $691.05       $763.0454   $763.05   $763.00   $763.10